Encoder, encoding method, decoder, and decoding method

ABSTRACT

An encoder which encodes a current block of a picture includes a processor and memory. Using the memory, the processor: determines whether intra prediction is to be used for the current block; and when it is determined that intra prediction is to be used for the current block, generates first transform coefficients by performing first transform of residual signals of the current block using a first transform basis; quantizes the first transform coefficients when an intra prediction mode for the current block is a determined mode and the first transform basis is different from a determined transform basis; and generates second transform coefficients by performing second transform of the first transform coefficients using a second transform basis, and quantizes the second transform coefficients, when the intra prediction mode for the current block is not the determined mode or when the first transform basis matches the determined transform basis.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. continuation application of PCT InternationalPatent Application Number PCT/JP2018/020656 filed on May 30, 2018,claiming the benefit of priority of U.S. Provisional Patent ApplicationNo. 62/513,637 filed on Jun. 1, 2017, the entire contents of which arehereby incorporated by reference.

BACKGROUND 1. Technical Field

The present disclosure relates to encoding and decoding of an image or avideo on a per block basis.

2. Description of the Related Art

A video coding standard called HEVC (high efficiency video coding) hasbeen standardized by JCT-VC (Joint Collaborative Team on Video Coding).

SUMMARY

An encoder according to an aspect of the present disclosure is anencoder which encodes a current block to be encoded of a pictureincludes a processor and memory. Using the memory, the processor:determines whether intra prediction is to be used for the current block;and when it is determined that intra prediction is to be used for thecurrent block, (i) generates first transform coefficients by performingfirst transform of residual signals of the current block using a firsttransform basis; (ii-1) quantizes the first transform coefficients whenan intra prediction mode for the current block is a determined mode andthe first transform basis is different from a determined transformbasis; and (ii-2) generates second transform coefficients by performingsecond transform of the first transform coefficients using a secondtransform basis, and quantizes the second transform coefficients, whenthe intra prediction mode for the current block is not the determinedmode or when the first transform basis matches the determined transformbasis.

These general and specific aspects may be implemented using a system, amethod, an integrated circuit, a computer program, or acomputer-readable recording medium such as a CD-ROM, or any combinationof systems, methods, integrated circuits, computer programs, orrecording media.

BRIEF DESCRIPTION OF DRAWINGS

These and other objects, advantages and features of the disclosure willbecome apparent from the following description thereof taken inconjunction with the accompanying drawings that illustrate a specificembodiment of the present disclosure.

FIG. 1 is a block diagram illustrating a functional configuration of anencoder according to Embodiment 1.

FIG. 2 illustrates one example of block splitting according toEmbodiment 1.

FIG. 3 is a chart indicating transform basis functions for eachtransform type.

FIG. 4A illustrates one example of a filter shape used in ALF.

FIG. 4B illustrates another example of a filter shape used in ALF.

FIG. 4C illustrates another example of a filter shape used in ALF.

FIG. 5A illustrates 67 intra prediction modes used in intra prediction.

FIG. 5B is a flow chart for illustrating an outline of a predictionimage correction process performed via OBMC processing.

FIG. 5C is a conceptual diagram for illustrating an outline of aprediction image correction process performed via OBMC processing.

FIG. 5D illustrates one example of FRUC.

FIG. 6 is for illustrating pattern matching (bilateral matching) betweentwo blocks along a motion trajectory.

FIG. 7 is for illustrating pattern matching (template matching) betweena template in the current picture and a block in a reference picture.

FIG. 8 is for illustrating a model assuming uniform linear motion.

FIG. 9A is for illustrating deriving a motion vector of each sub-blockbased on motion vectors of neighboring blocks.

FIG. 9B is for illustrating an outline of a process for deriving amotion vector via merge mode.

FIG. 9C is a conceptual diagram for illustrating an outline of DMVRprocessing.

FIG. 9D is for illustrating an outline of a prediction image generationmethod using a luminance correction process performed via LICprocessing.

FIG. 10 is a block diagram illustrating a functional configuration of adecoder according to Embodiment 1.

FIG. 11 is a flow chart illustrating transform and quantizationprocesses in an encoder according to Embodiment 2.

FIG. 12 is a flow chart illustrating inverse quantization and inversetransform processes in a decoder according to Embodiment 2.

FIG. 13 is a flow chart illustrating transform and quantizationprocesses in an encoder according to Embodiment 3.

FIG. 14 is a flow chart illustrating inverse quantization and inversetransform processes in a decoder according to Embodiment 3.

FIG. 15 is a flow chart illustrating transform and quantizationprocesses in an encoder according to Embodiment 4.

FIG. 16 is a flow chart illustrating encoding processes in the encoderaccording to Embodiment 4.

FIG. 17 is a flow chart illustrating decoding processes in a decoderaccording to Embodiment 4.

FIG. 18 is a flow chart illustrating inverse quantization and inversetransform processes in the decoder according to Embodiment 4.

FIG. 19 illustrates an overall configuration of a content providingsystem for implementing a content distribution service.

FIG. 20 illustrates one example of an encoding structure in scalableencoding.

FIG. 21 illustrates one example of an encoding structure in scalableencoding.

FIG. 22 illustrates an example of a display screen of a web page.

FIG. 23 illustrates an example of a display screen of a web page.

FIG. 24 illustrates one example of a smartphone.

FIG. 25 is a block diagram illustrating a configuration example of asmartphone.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments will be described specifically with referenceto the drawings.

It is to be noted that each of the embodiments described below indicatesa general or specific example. The numerical values, shapes, materials,constituent elements, the arrangement and connection of the constituentelements, steps, the processing order of the steps, etc., indicated inthe following exemplary embodiments are mere examples, and therefore donot limit the scope of the Claims. In addition, among the constituentelements in the following exemplary embodiments, constituent elementsnot recited in any one of the independent claims that define the mostgeneric concept are described as optional constituent elements.

Embodiment 1

First, an outline of Embodiment 1 will be presented. Embodiment 1 is oneexample of an encoder and a decoder to which the processes and/orconfigurations presented in subsequent description of aspects of thepresent disclosure are applicable. Note that Embodiment 1 is merely oneexample of an encoder and a decoder to which the processes and/orconfigurations presented in the description of aspects of the presentdisclosure are applicable. The processes and/or configurations presentedin the description of aspects of the present disclosure can also beimplemented in an encoder and a decoder different from those accordingto Embodiment 1.

When the processes and/or configurations presented in the description ofaspects of the present disclosure are applied to Embodiment 1, forexample, any of the following may be performed.

(1) regarding the encoder or the decoder according to Embodiment 1,among components included in the encoder or the decoder according to

Embodiment 1, substituting a component corresponding to a componentpresented in the description of aspects of the present disclosure with acomponent presented in the description of aspects of the presentdisclosure;

(2) regarding the encoder or the decoder according to Embodiment 1,implementing discretionary changes to functions or implemented processesperformed by one or more components included in the encoder or thedecoder according to Embodiment 1, such as addition, substitution, orremoval, etc., of such functions or implemented processes, thensubstituting a component corresponding to a component presented in thedescription of aspects of the present disclosure with a componentpresented in the description of aspects of the present disclosure;

(3) regarding the method implemented by the encoder or the decoderaccording to Embodiment 1, implementing discretionary changes such asaddition of processes and/or substitution, removal of one or more of theprocesses included in the method, and then substituting a processescorresponding to a process presented in the description of aspects ofthe present disclosure with a process presented in the description ofaspects of the present disclosure;

(4) combining one or more components included in the encoder or thedecoder according to Embodiment 1 with a component presented in thedescription of aspects of the present disclosure, a component includingone or more functions included in a component presented in thedescription of aspects of the present disclosure, or a component thatimplements one or more processes implemented by a component presented inthe description of aspects of the present disclosure;

(5) combining a component including one or more functions included inone or more components included in the encoder or the decoder accordingto Embodiment 1, or a component that implements one or more processesimplemented by one or more components included in the encoder or thedecoder according to Embodiment 1 with a component presented in thedescription of aspects of the present disclosure, a component includingone or more functions included in a component presented in thedescription of aspects of the present disclosure, or a component thatimplements one or more processes implemented by a component presented inthe description of aspects of the present disclosure;

(6) regarding the method implemented by the encoder or the decoderaccording to Embodiment 1, among processes included in the method,substituting a process corresponding to a process presented in thedescription of aspects of the present disclosure with a processpresented in the description of aspects of the present disclosure; and

(7) combining one or more processes included in the method implementedby the encoder or the decoder according to Embodiment 1 with a processpresented in the description of aspects of the present disclosure.

Note that the implementation of the processes and/or configurationspresented in the description of aspects of the present disclosure is notlimited to the above examples. For example, the processes and/orconfigurations presented in the description of aspects of the presentdisclosure may be implemented in a device used for a purpose differentfrom the moving picture/picture encoder or the moving picture/picturedecoder disclosed in Embodiment 1. Moreover, the processes and/orconfigurations presented in the description of aspects of the presentdisclosure may be independently implemented. Moreover, processes and/orconfigurations described in different aspects may be combined.

[Encoder Outline]

First, the encoder according to Embodiment 1 will be outlined. FIG. 1 isa block diagram illustrating a functional configuration of encoder 100according to Embodiment 1. Encoder 100 is a moving picture/pictureencoder that encodes a moving picture/picture block by block.

As illustrated in FIG. 1, encoder 100 is a device that encodes a pictureblock by block, and includes splitter 102, subtractor 104, transformer106, quantizer 108, entropy encoder 110, inverse quantizer 112, inversetransformer 114, adder 116, block memory 118, loop filter 120, framememory 122, intra predictor 124, inter predictor 126, and predictioncontroller 128.

Encoder 100 is realized as, for example, a generic processor and memory.In this case, when a software program stored in the memory is executedby the processor, the processor functions as splitter 102, subtractor104, transformer 106, quantizer 108, entropy encoder 110, inversequantizer 112, inverse transformer 114, adder 116, loop filter 120,intra predictor 124, inter predictor 126, and prediction controller 128.Alternatively, encoder 100 may be realized as one or more dedicatedelectronic circuits corresponding to splitter 102, subtractor 104,transformer 106, quantizer 108, entropy encoder 110, inverse quantizer112, inverse transformer 114, adder 116, loop filter 120, intrapredictor 124, inter predictor 126, and prediction controller 128.

Hereinafter, each component included in encoder 100 will be described.

[Splitter]

Splitter 102 splits each picture included in an input moving pictureinto blocks, and outputs each block to subtractor 104. For example,splitter 102 first splits a picture into blocks of a fixed size (forexample, 128×128). The fixed size block is also referred to as codingtree unit (CTU). Splitter 102 then splits each fixed size block intoblocks of variable sizes (for example, 64×64 or smaller), based onrecursive quadtree and/or binary tree block splitting. The variable sizeblock is also referred to as a coding unit (CU), a prediction unit (PU),or a transform unit (TU). Note that in this embodiment, there is no needto differentiate between CU, PU, and TU; all or some of the blocks in apicture may be processed per CU, PU, or TU.

FIG. 2 illustrates one example of block splitting according toEmbodiment 1. In FIG. 2, the solid lines represent block boundaries ofblocks split by quadtree block splitting, and the dashed lines representblock boundaries of blocks split by binary tree block splitting.

Here, block 10 is a square 128×128 pixel block (128×128 block). This128×128 block 10 is first split into four square 64×64 blocks (quadtreeblock splitting).

The top left 64×64 block is further vertically split into two rectangle32×64 blocks, and the left 32×64 block is further vertically split intotwo rectangle 16×64 blocks (binary tree block splitting). As a result,the top left 64×64 block is split into two 16×64 blocks 11 and 12 andone 32×64 block 13.

The top right 64×64 block is horizontally split into two rectangle 64×32blocks 14 and 15 (binary tree block splitting).

The bottom left 64×64 block is first split into four square 32×32 blocks(quadtree block splitting). The top left block and the bottom rightblock among the four 32×32 blocks are further split. The top left 32×32block is vertically split into two rectangle 16×32 blocks, and the right16×32 block is further horizontally split into two 16×16 blocks (binarytree block splitting). The bottom right 32×32 block is horizontallysplit into two 32×16 blocks (binary tree block splitting). As a result,the bottom left 64×64 block is split into 16×32 block 16, two 16×16blocks 17 and 18, two 32×32 blocks 19 and 20, and two 32×16 blocks 21and 22.

The bottom right 64×64 block 23 is not split.

As described above, in FIG. 2, block 10 is split into 13 variable sizeblocks 11 through 23 based on recursive quadtree and binary tree blocksplitting. This type of splitting is also referred to as quadtree plusbinary tree (QTBT) splitting.

Note that in FIG. 2, one block is split into four or two blocks(quadtree or binary tree block splitting), but splitting is not limitedto this example. For example, one block may be split into three blocks(ternary block splitting). Splitting including such ternary blocksplitting is also referred to as multi-type tree (MBT) splitting.

[Subtractor]

Subtractor 104 subtracts a prediction signal (prediction sample) from anoriginal signal (original sample) per block split by splitter 102. Inother words, subtractor 104 calculates prediction errors (also referredto as residuals) of a block to be encoded (hereinafter referred to as acurrent block). Subtractor 104 then outputs the calculated predictionerrors to transformer 106.

The original signal is a signal input into encoder 100, and is a signalrepresenting an image for each picture included in a moving picture (forexample, a luma signal and two chroma signals). Hereinafter, a signalrepresenting an image is also referred to as a sample.

[Transformer]

Transformer 106 transforms spatial domain prediction errors intofrequency domain transform coefficients, and outputs the transformcoefficients to quantizer 108. More specifically, transformer 106applies, for example, a predefined discrete cosine transform (DCT) ordiscrete sine transform (DST) to spatial domain prediction errors.

Note that transformer 106 may adaptively select a transform type fromamong a plurality of transform types, and transform prediction errorsinto transform coefficients by using a transform basis functioncorresponding to the selected transform type. This sort of transform isalso referred to as explicit multiple core transform (EMT) or adaptivemultiple transform (AMT).

The transform types include, for example, DCT-II, DCT-V, DCT-VIII,DST-I, and DST-VII. FIG. 3 is a chart indicating transform basisfunctions for each transform type. In FIG. 3, N indicates the number ofinput pixels. For example, selection of a transform type from among theplurality of transform types may depend on the prediction type (intraprediction and inter prediction), and may depend on intra predictionmode.

Information indicating whether to apply such EMT or AMT (referred to as,for example, an AMT flag) and information indicating the selectedtransform type is signalled at the CU level. Note that the signaling ofsuch information need not be performed at the CU level, and may beperformed at another level (for example, at the sequence level, picturelevel, slice level, tile level, or CTU level).

Moreover, transformer 106 may apply a secondary transform to thetransform coefficients (transform result). Such a secondary transform isalso referred to as adaptive secondary transform (AST) or non-separablesecondary transform (NSST). For example, transformer 106 applies asecondary transform to each sub-block (for example, each 4×4 sub-block)included in the block of the transform coefficients corresponding to theintra prediction errors. Information indicating whether to apply NSSTand information related to the transform matrix used in NSST aresignalled at the CU level. Note that the signaling of such informationneed not be performed at the CU level, and may be performed at anotherlevel (for example, at the sequence level, picture level, slice level,tile level, or CTU level).

Here, a separable transform is a method in which a transform isperformed a plurality of times by separately performing a transform foreach direction according to the number of dimensions input. Anon-separable transform is a method of performing a collective transformin which two or more dimensions in a multidimensional input arecollectively regarded as a single dimension.

In one example of a non-separable transform, when the input is a 4×4block, the 4×4 block is regarded as a single array including 16components, and the transform applies a 16×16 transform matrix to thearray.

Moreover, similar to above, after an input 4×4 block is regarded as asingle array including 16 components, a transform that performs aplurality of Givens rotations on the array (i.e., a Hypercube-GivensTransform) is also one example of a nonseparable transform.

[Quantizer]

Quantizer 108 quantizes the transform coefficients output fromtransformer 106. More specifically, quantizer 108 scans, in apredetermined scanning order, the transform coefficients of the currentblock, and quantizes the scanned transform coefficients based onquantization parameters (QP) corresponding to the transformcoefficients. Quantizer 108 then outputs the quantized transformcoefficients (hereinafter referred to as quantized coefficients) of thecurrent block to entropy encoder 110 and inverse quantizer 112.

A predetermined order is an order for quantizing/inverse quantizingtransform coefficients. For example, a predetermined scanning order isdefined as ascending order of frequency (from low to high frequency) ordescending order of frequency (from high to low frequency).

A quantization parameter is a parameter defining a quantization stepsize (quantization width). For example, if the value of the quantizationparameter increases, the quantization step size also increases. In otherwords, if the value of the quantization parameter increases, thequantization error increases.

[Entropy Encoder]

Entropy encoder 110 generates an encoded signal (encoded bitstream) byvariable length encoding quantized coefficients, which are inputs fromquantizer 108. More specifically, entropy encoder 110, for example,binarizes quantized coefficients and arithmetic encodes the binarysignal.

[Inverse Quantizer]

Inverse quantizer 112 inverse quantizes quantized coefficients, whichare inputs from quantizer 108. More specifically, inverse quantizer 112inverse quantizes, in a predetermined scanning order, quantizedcoefficients of the current block. Inverse quantizer 112 then outputsthe inverse quantized transform coefficients of the current block toinverse transformer 114.

[Inverse Transformer]

Inverse transformer 114 restores prediction errors by inversetransforming transform coefficients, which are inputs from inversequantizer 112. More specifically, inverse transformer 114 restores theprediction errors of the current block by applying an inverse transformcorresponding to the transform applied by transformer 106 on thetransform coefficients. Inverse transformer 114 then outputs therestored prediction errors to adder 116.

Note that since information is lost in quantization, the restoredprediction errors do not match the prediction errors calculated bysubtractor 104. In other words, the restored prediction errors includequantization errors.

[Adder]

Adder 116 reconstructs the current block by summing prediction errors,which are inputs from inverse transformer 114, and prediction samples,which are inputs from prediction controller 128. Adder 116 then outputsthe reconstructed block to block memory 118 and loop filter 120. Areconstructed block is also referred to as a local decoded block.

[Block Memory]

Block memory 118 is storage for storing blocks in a picture to beencoded (hereinafter referred to as a current picture) for reference inintra prediction. More specifically, block memory 118 storesreconstructed blocks output from adder 116.

[Loop Filter]

Loop filter 120 applies a loop filter to blocks reconstructed by adder116, and outputs the filtered reconstructed blocks to frame memory 122.A loop filter is a filter used in an encoding loop (in-loop filter), andincludes, for example, a deblocking filter (DF), a sample adaptiveoffset (SAO), and an adaptive loop filter (ALF).

In ALF, a least square error filter for removing compression artifactsis applied. For example, one filter from among a plurality of filters isselected for each 2×2 sub-block in the current block based on directionand activity of local gradients, and is applied.

More specifically, first, each sub-block (for example, each 2×2sub-block) is categorized into one out of a plurality of classes (forexample, 15 or 25 classes). The classification of the sub-block is basedon gradient directionality and activity. For example, classificationindex C is derived based on gradient directionality D (for example, 0 to2 or 0 to 4) and gradient activity A (for example, 0 to 4) (for example,C=5D+A). Then, based on classification index C, each sub-block iscategorized into one out of a plurality of classes (for example, 15 or25 classes).

For example, gradient directionality D is calculated by comparinggradients of a plurality of directions (for example, the horizontal,vertical, and two diagonal directions). Moreover, for example, gradientactivity A is calculated by summing gradients of a plurality ofdirections and quantizing the sum.

The filter to be used for each sub-block is determined from among theplurality of filters based on the result of such categorization.

The filter shape to be used in ALF is, for example, a circular symmetricfilter shape. FIG. 4A through FIG. 4C illustrate examples of filtershapes used in ALF. FIG. 4A illustrates a 5×5 diamond shape filter, FIG.4B illustrates a 7×7 diamond shape filter, and FIG. 4C illustrates a 9×9diamond shape filter. Information indicating the filter shape issignalled at the picture level. Note that the signaling of informationindicating the filter shape need not be performed at the picture level,and may be performed at another level (for example, at the sequencelevel, slice level, tile level, CTU level, or CU level).

The enabling or disabling of ALF is determined at the picture level orCU level. For example, for luma, the decision to apply ALF or not isdone at the CU level, and for chroma, the decision to apply ALF or notis done at the picture level. Information indicating whether ALF isenabled or disabled is signalled at the picture level or CU level. Notethat the signaling of information indicating whether ALF is enabled ordisabled need not be performed at the picture level or CU level, and maybe performed at another level (for example, at the sequence level, slicelevel, tile level, or CTU level).

The coefficients set for the plurality of selectable filters (forexample, 15 or 25 filters) is signalled at the picture level. Note thatthe signaling of the coefficients set need not be performed at thepicture level, and may be performed at another level (for example, atthe sequence level, slice level, tile level, CTU level, CU level, orsub-block level).

[Frame Memory]

Frame memory 122 is storage for storing reference pictures used in interprediction, and is also referred to as a frame buffer. Morespecifically, frame memory 122 stores reconstructed blocks filtered byloop filter 120.

[Intra Predictor]

Intra predictor 124 generates a prediction signal (intra predictionsignal) by intra predicting the current block with reference to a blockor blocks in the current picture and stored in block memory 118 (alsoreferred to as intra frame prediction). More specifically, intrapredictor 124 generates an intra prediction signal by intra predictionwith reference to samples (for example, luma and/or chroma values) of ablock or blocks neighboring the current block, and then outputs theintra prediction signal to prediction controller 128.

For example, intra predictor 124 performs intra prediction by using onemode from among a plurality of predefined intra prediction modes. Theintra prediction modes include one or more non-directional predictionmodes and a plurality of directional prediction modes.

The one or more non-directional prediction modes include, for example,planar prediction mode and DC prediction mode defined in theH.265/high-efficiency video coding (HEVC) standard (see NPL 1: H.265(ISO/IEC 23008-2 HEVC (High Efficiency Video Coding))). The plurality ofdirectional prediction modes include, for example, the 33 directionalprediction modes defined in the H.265/HEVC standard. Note that theplurality of directional prediction modes may further include 32directional prediction modes in addition to the 33 directionalprediction modes (for a total of 65 directional prediction modes). FIG.5A illustrates 67 intra prediction modes used in intra prediction (twonon-directional prediction modes and 65 directional prediction modes).The solid arrows represent the 33 directions defined in the H.265/HEVCstandard, and the dashed arrows represent the additional 32 directions.

Note that a luma block may be referenced in chroma block intraprediction. In other words, a chroma component of the current block maybe predicted based on a luma component of the current block. Such intraprediction is also referred to as cross-component linear model (CCLM)prediction. Such a chroma block intra prediction mode that references aluma block (referred to as, for example, CCLM mode) may be added as oneof the chroma block intra prediction modes.

Intra predictor 124 may correct post-intra-prediction pixel values basedon horizontal/vertical reference pixel gradients. Intra predictionaccompanied by this sort of correcting is also referred to as positiondependent intra prediction combination (PDPC). Information indicatingwhether to apply PDPC or not (referred to as, for example, a PDPC flag)is, for example, signalled at the CU level. Note that the signaling ofthis information need not be performed at the CU level, and may beperformed at another level (for example, on the sequence level, picturelevel, slice level, tile level, or CTU level).

[Inter Predictor]

Inter predictor 126 generates a prediction signal (inter predictionsignal) by inter predicting the current block with reference to a blockor blocks in a reference picture, which is different from the currentpicture and is stored in frame memory 122 (also referred to as interframe prediction). Inter prediction is performed per current block orper sub-block (for example, per 4x4 block) in the current block. Forexample, inter predictor 126 performs motion estimation in a referencepicture for the current block or sub-block. Inter predictor 126 thengenerates an inter prediction signal of the current block or sub-blockby motion compensation by using motion information (for example, amotion vector) obtained from motion estimation. Inter predictor 126 thenoutputs the generated inter prediction signal to prediction controller128.

The motion information used in motion compensation is signalled. Amotion vector predictor may be used for the signaling of the motionvector. In other words, the difference between the motion vector and themotion vector predictor may be signalled.

Note that the inter prediction signal may be generated using motioninformation for a neighboring block in addition to motion informationfor the current block obtained from motion estimation. Morespecifically, the inter prediction signal may be generated per sub-blockin the current block by calculating a weighted sum of a predictionsignal based on motion information obtained from motion estimation and aprediction signal based on motion information for a neighboring block.Such inter prediction (motion compensation) is also referred to asoverlapped block motion compensation (OBMC).

In such an OBMC mode, information indicating sub-block size for OBMC(referred to as, for example, OBMC block size) is signalled at thesequence level. Moreover, information indicating whether to apply theOBMC mode or not (referred to as, for example, an OBMC flag) issignalled at the CU level. Note that the signaling of such informationneed not be performed at the sequence level and CU level, and may beperformed at another level (for example, at the picture level, slicelevel, tile level, CTU level, or sub-block level).

Hereinafter, the OBMC mode will be described in further detail. FIG. 5Bis a flowchart and FIG. 5C is a conceptual diagram for illustrating anoutline of a prediction image correction process performed via OBMCprocessing.

First, a prediction image (Pred) is obtained through typical motioncompensation using a motion vector (MV) assigned to the current block.

Next, a prediction image (Pred_L) is obtained by applying a motionvector (MV_L) of the encoded neighboring left block to the currentblock, and a first pass of the correction of the prediction image ismade by superimposing the prediction image and Pred_L.

Similarly, a prediction image (Pred_U) is obtained by applying a motionvector (MV_U) of the encoded neighboring upper block to the currentblock, and a second pass of the correction of the prediction image ismade by superimposing the prediction image resulting from the first passand Pred_U. The result of the second pass is the final prediction image.

Note that the above example is of a two-pass correction method using theneighboring left and upper blocks, but the method may be a three-pass orhigher correction method that also uses the neighboring right and/orlower block.

Note that the region subject to superimposition may be the entire pixelregion of the block, and, alternatively, may be a partial block boundaryregion.

Note that here, the prediction image correction process is described asbeing based on a single reference picture, but the same applies when aprediction image is corrected based on a plurality of referencepictures. In such a case, after corrected prediction images resultingfrom performing correction based on each of the reference pictures areobtained, the obtained corrected prediction images are furthersuperimposed to obtain the final prediction image.

Note that the unit of the current block may be a prediction block and,alternatively, may be a sub-block obtained by further dividing theprediction block.

One example of a method for determining whether to implement OBMCprocessing is by using an obmc_flag, which is a signal that indicateswhether to implement OBMC processing. As one specific example, theencoder determines whether the current block belongs to a regionincluding complicated motion. The encoder sets the obmc_flag to a valueof “1” when the block belongs to a region including complicated motionand implements OBMC processing when encoding, and sets the obmc_flag toa value of “0” when the block does not belong to a region includingcomplication motion and encodes without implementing OBMC processing.The decoder switches between implementing OBMC processing or not bydecoding the obmc_flag written in the stream and performing the decodingin accordance with the flag value.

Note that the motion information may be derived on the decoder sidewithout being signalled. For example, a merge mode defined in theH.265/HEVC standard may be used. Moreover, for example, the motioninformation may be derived by performing motion estimation on thedecoder side. In this case, motion estimation is performed without usingthe pixel values of the current block.

Here, a mode for performing motion estimation on the decoder side willbe described. A mode for performing motion estimation on the decoderside is also referred to as pattern matched motion vector derivation(PMMVD) mode or frame rate up-conversion (FRUC) mode.

One example of FRUC processing is illustrated in FIG. 5D. First, acandidate list (a candidate list may be a merge list) of candidates eachincluding a motion vector predictor is generated with reference tomotion vectors of encoded blocks that spatially or temporally neighborthe current block. Next, the best candidate MV is selected from among aplurality of candidate MVs registered in the candidate list. Forexample, evaluation values for the candidates included in the candidatelist are calculated and one candidate is selected based on thecalculated evaluation values.

Next, a motion vector for the current block is derived from the motionvector of the selected candidate. More specifically, for example, themotion vector for the current block is calculated as the motion vectorof the selected candidate (best candidate MV), as-is. Alternatively, themotion vector for the current block may be derived by pattern matchingperformed in the vicinity of a position in a reference picturecorresponding to the motion vector of the selected candidate. In otherwords, when the vicinity of the best candidate MV is searched via thesame method and an MV having a better evaluation value is found, thebest candidate MV may be updated to the MV having the better evaluationvalue, and the MV having the better evaluation value may be used as thefinal MV for the current block. Note that a configuration in which thisprocessing is not implemented is also acceptable.

The same processes may be performed in cases in which the processing isperformed in units of sub-blocks.

Note that an evaluation value is calculated by calculating thedifference in the reconstructed image by pattern matching performedbetween a region in a reference picture corresponding to a motion vectorand a predetermined region. Note that the evaluation value may becalculated by using some other information in addition to thedifference.

The pattern matching used is either first pattern matching or secondpattern matching. First pattern matching and second pattern matching arealso referred to as bilateral matching and template matching,respectively.

In the first pattern matching, pattern matching is performed between twoblocks along the motion trajectory of the current block in two differentreference pictures. Therefore, in the first pattern matching, a regionin another reference picture conforming to the motion trajectory of thecurrent block is used as the predetermined region for theabove-described calculation of the candidate evaluation value.

FIG. 6 is for illustrating one example of pattern matching (bilateralmatching) between two blocks along a motion trajectory. As illustratedin FIG. 6, in the first pattern matching, two motion vectors (MV0, MV1)are derived by finding the best match between two blocks along themotion trajectory of the current block (Cur block) in two differentreference pictures (Ref0, Ref1). More specifically, a difference between(i) a reconstructed image in a specified position in a first encodedreference picture (Ref0) specified by a candidate MV and (ii) areconstructed picture in a specified position in a second encodedreference picture (Ref1) specified by a symmetrical MV scaled at adisplay time interval of the candidate MV may be derived, and theevaluation value for the current block may be calculated by using thederived difference. The candidate MV having the best evaluation valueamong the plurality of candidate MVs may be selected as the final MV.

Under the assumption of continuous motion trajectory, the motion vectors(MV0, MV1) pointing to the two reference blocks shall be proportional tothe temporal distances (TD0, TD1) between the current picture (Cur Pic)and the two reference pictures (Ref0, Ref1). For example, when thecurrent picture is temporally between the two reference pictures and thetemporal distance from the current picture to the two reference picturesis the same, the first pattern matching derives a mirror basedbi-directional motion vector.

In the second pattern matching, pattern matching is performed between atemplate in the current picture (blocks neighboring the current block inthe current picture (for example, the top and/or left neighboringblocks)) and a block in a reference picture. Therefore, in the secondpattern matching, a block neighboring the current block in the currentpicture is used as the predetermined region for the above-describedcalculation of the candidate evaluation value.

FIG. 7 is for illustrating one example of pattern matching (templatematching) between a template in the current picture and a block in areference picture. As illustrated in FIG. 7, in the second patternmatching, a motion vector of the current block is derived by searching areference picture (Ref0) to find the block that best matches neighboringblocks of the current block (Cur block) in the current picture (CurPic). More specifically, a difference between (i) a reconstructed imageof an encoded region that is both or one of the neighboring left andneighboring upper region and (ii) a reconstructed picture in the sameposition in an encoded reference picture (Ref0) specified by a candidateMV may be derived, and the evaluation value for the current block may becalculated by using the derived difference. The candidate MV having thebest evaluation value among the plurality of candidate MVs may beselected as the best candidate MV.

Information indicating whether to apply the FRUC mode or not (referredto as, for example, a FRUC flag) is signalled at the CU level. Moreover,when the FRUC mode is applied (for example, when the FRUC flag is set totrue), information indicating the pattern matching method (first patternmatching or second pattern matching) is signalled at the CU level. Notethat the signaling of such information need not be performed at the CUlevel, and may be performed at another level (for example, at thesequence level, picture level, slice level, tile level, CTU level, orsub-block level).

Here, a mode for deriving a motion vector based on a model assuminguniform linear motion will be described. This mode is also referred toas a bi-directional optical flow (BIO) mode.

FIG. 8 is for illustrating a model assuming uniform linear motion. InFIG. 8, (v_(x), v_(y)) denotes a velocity vector, and τ₀ and τ₁ denotetemporal distances between the current picture (Cur Pic) and tworeference pictures (Ref₀, Ref₁) (MVx₀, MVy₀) denotes a motion vectorcorresponding to reference picture Ref₀, and (MVx₁, MVy₁) denotes amotion vector corresponding to reference picture Ref₁.

Here, under the assumption of uniform linear motion exhibited byvelocity vector (v_(x), v_(y)), (MVx₀, MVy₀) and (MVx₁, MVy₁) arerepresented as (v_(x)τ₀, v_(y)τ₀) and (−v_(x)τ₁, −v_(y)τ₁),respectively, and the following optical flow equation is given.

MATH. 1

∂I ^((k)) /∂t+v _(x) ∂I ^((k)) /∂x+v _(y) ∂I ^((k)) /∂y=0   (1)

Here, I^((k)) denotes a luma value from reference picture k (k=0, 1)after motion compensation. This optical flow equation shows that the sumof (i) the time derivative of the luma value, (ii) the product of thehorizontal velocity and the horizontal component of the spatial gradientof a reference picture, and (iii) the product of the vertical velocityand the vertical component of the spatial gradient of a referencepicture is equal to zero. A motion vector of each block obtained from,for example, a merge list is corrected pixel by pixel based on acombination of the optical flow equation and Hermite interpolation.

Note that a motion vector may be derived on the decoder side using amethod other than deriving a motion vector based on a model assuminguniform linear motion. For example, a motion vector may be derived foreach sub-block based on motion vectors of neighboring blocks.

Here, a mode in which a motion vector is derived for each sub-blockbased on motion vectors of neighboring blocks will be described. Thismode is also referred to as affine motion compensation prediction mode.

FIG. 9A is for illustrating deriving a motion vector of each sub-blockbased on motion vectors of neighboring blocks. In FIG. 9A, the currentblock includes 16 4×4 sub-blocks. Here, motion vector v₀ of the top leftcorner control point in the current block is derived based on motionvectors of neighboring sub-blocks, and motion vector v₁ of the top rightcorner control point in the current block is derived based on motionvectors of neighboring blocks. Then, using the two motion vectors v₀ andv₁, the motion vector (v_(x), v_(y)) of each sub-block in the currentblock is derived using Equation 2 below.

MATH. 2

$\begin{matrix}{{MATH}.\mspace{14mu} 2} & \; \\\left\{ \begin{matrix}{v_{x} = {{\frac{\left( {v_{1x} - v_{0x}} \right)}{w}x} - {\frac{\left( {v_{1y} - v_{0y}} \right)}{w}y} + v_{0x}}} \\{v_{y} = {{\frac{\left( {v_{1y} - v_{0y}} \right)}{w}x} - {\frac{\left( {v_{1x} - v_{0x}} \right)}{w}y} + v_{0y}}}\end{matrix} \right. & (2)\end{matrix}$

Here, x and y are the horizontal and vertical positions of thesub-block, respectively, and w is a predetermined weighted coefficient.

Such an affine motion compensation prediction mode may include a numberof modes of different methods of deriving the motion vectors of the topleft and top right corner control points. Information indicating such anaffine motion compensation prediction mode (referred to as, for example,an affine flag) is signalled at the CU level. Note that the signaling ofinformation indicating the affine motion compensation prediction modeneed not be performed at the CU level, and may be performed at anotherlevel (for example, at the sequence level, picture level, slice level,tile level, CTU level, or sub-block level).

[Prediction Controller]

Prediction controller 128 selects either the intra prediction signal orthe inter prediction signal, and outputs the selected prediction signalto subtractor 104 and adder 116.

Here, an example of deriving a motion vector via merge mode in a currentpicture will be given. FIG. 9B is for illustrating an outline of aprocess for deriving a motion vector via merge mode.

First, an MV predictor list in which candidate MV predictors areregistered is generated. Examples of candidate MV predictors include:spatially neighboring MV predictors, which are MVs of encoded blockspositioned in the spatial vicinity of the current block; a temporallyneighboring MV predictor, which is an MV of a block in an encodedreference picture that neighbors a block in the same location as thecurrent block; a combined MV predictor, which is an MV generated bycombining the MV values of the spatially neighboring MV predictor andthe temporally neighboring MV predictor; and a zero MV predictor, whichis an MV whose value is zero.

Next, the MV of the current block is determined by selecting one MVpredictor from among the plurality of MV predictors registered in the MVpredictor list.

Furthermore, in the variable-length encoder, a merge_idx, which is asignal indicating which MV predictor is selected, is written and encodedinto the stream.

Note that the MV predictors registered in the MV predictor listillustrated in FIG. 9B constitute one example. The number of MVpredictors registered in the MV predictor list may be different from thenumber illustrated in FIG. 9B, the MV predictors registered in the MVpredictor list may omit one or more of the types of MV predictors givenin the example in FIG. 9B, and the MV predictors registered in the MVpredictor list may include one or more types of MV predictors inaddition to and different from the types given in the example in FIG.9B.

Note that the final MV may be determined by performing DMVR processing(to be described later) by using the MV of the current block derived viamerge mode.

Here, an example of determining an MV by using DMVR processing will begiven.

FIG. 9C is a conceptual diagram for illustrating an outline of DMVRprocessing.

First, the most appropriate MVP set for the current block is consideredto be the candidate MV, reference pixels are obtained from a firstreference picture, which is a picture processed in the L0 direction inaccordance with the candidate MV, and a second reference picture, whichis a picture processed in the L1 direction in accordance with thecandidate MV, and a template is generated by calculating the average ofthe reference pixels.

Next, using the template, the surrounding regions of the candidate MVsof the first and second reference pictures are searched, and the MV withthe lowest cost is determined to be the final MV. Note that the costvalue is calculated using, for example, the difference between eachpixel value in the template and each pixel value in the regionssearched, as well as the MV value.

Note that the outlines of the processes described here are fundamentallythe same in both the encoder and the decoder.

Note that processing other than the processing exactly as describedabove may be used, so long as the processing is capable of deriving thefinal MV by searching the surroundings of the candidate MV.

Here, an example of a mode that generates a prediction image by usingLIC processing will be given.

FIG. 9D is for illustrating an outline of a prediction image generationmethod using a luminance correction process performed via LICprocessing.

First, an MV is extracted for obtaining, from an encoded referencepicture, a reference image corresponding to the current block.

Next, information indicating how the luminance value changed between thereference picture and the current picture is extracted and a luminancecorrection parameter is calculated by using the luminance pixel valuesfor the encoded left neighboring reference region and the encoded upperneighboring reference region, and the luminance pixel value in the samelocation in the reference picture specified by the MV.

The prediction image for the current block is generated by performing aluminance correction process by using the luminance correction parameteron the reference image in the reference picture specified by the MV Notethat the shape of the surrounding reference region illustrated in

FIG. 9D is just one example; the surrounding reference region may have adifferent shape.

Moreover, although a prediction image is generated from a singlereference picture in this example, in cases in which a prediction imageis generated from a plurality of reference pictures as well, theprediction image is generated after performing a luminance correctionprocess, via the same method, on the reference images obtained from thereference pictures.

One example of a method for determining whether to implement LICprocessing is by using an lic_flag, which is a signal that indicateswhether to implement LIC processing. As one specific example, theencoder determines whether the current block belongs to a region ofluminance change. The encoder sets the lic_flag to a value of “1” whenthe block belongs to a region of luminance change and implements LICprocessing when encoding, and sets the lic_flag to a value of “0” whenthe block does not belong to a region of luminance change and encodeswithout implementing LIC processing. The decoder switches betweenimplementing LIC processing or not by decoding the lic_flag written inthe stream and performing the decoding in accordance with the flagvalue.

One example of a different method of determining whether to implementLIC processing is determining so in accordance with whether LICprocessing was determined to be implemented for a surrounding block. Inone specific example, when merge mode is used on the current block,whether LIC processing was applied in the encoding of the surroundingencoded block selected upon deriving the MV in the merge mode processingmay be determined, and whether to implement LIC processing or not can beswitched based on the result of the determination. Note that in thisexample, the same applies to the processing performed on the decoderside.

[Decoder Outline]

Next, a decoder capable of decoding an encoded signal (encodedbitstream) output from encoder 100 will be described. FIG. 10 is a blockdiagram illustrating a functional configuration of decoder 200 accordingto Embodiment 1. Decoder 200 is a moving picture/picture decoder thatdecodes a moving picture/picture block by block.

As illustrated in FIG. 10, decoder 200 includes entropy decoder 202,inverse quantizer 204, inverse transformer 206, adder 208, block memory210, loop filter 212, frame memory 214, intra predictor 216, interpredictor 218, and prediction controller 220.

Decoder 200 is realized as, for example, a generic processor and memory.In this case, when a software program stored in the memory is executedby the processor, the processor functions as entropy decoder 202,inverse quantizer 204, inverse transformer 206, adder 208, loop filter212, intra predictor 216, inter predictor 218, and prediction controller220. Alternatively, decoder 200 may be realized as one or more dedicatedelectronic circuits corresponding to entropy decoder 202, inversequantizer 204, inverse transformer 206, adder 208, loop filter 212,intra predictor 216, inter predictor 218, and prediction controller 220.

Hereinafter, each component included in decoder 200 will be described.

[Entropy Decoder]

Entropy decoder 202 entropy decodes an encoded bitstream. Morespecifically, for example, entropy decoder 202 arithmetic decodes anencoded bitstream into a binary signal. Entropy decoder 202 thendebinarizes the binary signal. With this, entropy decoder 202 outputsquantized coefficients of each block to inverse quantizer 204.

[Inverse Quantizer]

Inverse quantizer 204 inverse quantizes quantized coefficients of ablock to be decoded (hereinafter referred to as a current block), whichare inputs from entropy decoder 202. More specifically, inversequantizer 204 inverse quantizes quantized coefficients of the currentblock based on quantization parameters corresponding to the quantizedcoefficients. Inverse quantizer 204 then outputs the inverse quantizedcoefficients (i.e., transform coefficients) of the current block toinverse transformer 206.

[Inverse Transformer]

Inverse transformer 206 restores prediction errors by inversetransforming transform coefficients, which are inputs from inversequantizer 204.

For example, when information parsed from an encoded bitstream indicatesapplication of EMT or AMT (for example, when the AMT flag is set totrue), inverse transformer 206 inverse transforms the transformcoefficients of the current block based on information indicating theparsed transform type.

Moreover, for example, when information parsed from an encoded bitstreamindicates application of NSST, inverse transformer 206 applies asecondary inverse transform to the transform coefficients.

[Adder]

Adder 208 reconstructs the current block by summing prediction errors,which are inputs from inverse transformer 206, and prediction samples,which is an input from prediction controller 220. Adder 208 then outputsthe reconstructed block to block memory 210 and loop filter 212.

[Block Memory]

Block memory 210 is storage for storing blocks in a picture to bedecoded (hereinafter referred to as a current picture) for reference inintra prediction. More specifically, block memory 210 storesreconstructed blocks output from adder 208.

[Loop Filter]

Loop filter 212 applies a loop filter to blocks reconstructed by adder208, and outputs the filtered reconstructed blocks to frame memory 214and, for example, a display device.

When information indicating the enabling or disabling of ALF parsed froman encoded bitstream indicates enabled, one filter from among aplurality of filters is selected based on direction and activity oflocal gradients, and the selected filter is applied to the reconstructedblock.

[Frame Memory]

Frame memory 214 is storage for storing reference pictures used in interprediction, and is also referred to as a frame buffer. Morespecifically, frame memory 214 stores reconstructed blocks filtered byloop filter 212.

[Intra Predictor]

Intra predictor 216 generates a prediction signal (intra predictionsignal) by intra prediction with reference to a block or blocks in thecurrent picture and stored in block memory 210. More specifically, intrapredictor 216 generates an intra prediction signal by intra predictionwith reference to samples (for example, luma and/or chroma values) of ablock or blocks neighboring the current block, and then outputs theintra prediction signal to prediction controller 220.

Note that when an intra prediction mode in which a chroma block is intrapredicted from a luma block is selected, intra predictor 216 may predictthe chroma component of the current block based on the luma component ofthe current block.

Moreover, when information indicating the application of PDPC is parsedfrom an encoded bitstream, intra predictor 216 correctspost-intra-prediction pixel values based on horizontal/verticalreference pixel gradients.

[Inter Predictor]

Inter predictor 218 predicts the current block with reference to areference picture stored in frame memory 214. Inter prediction isperformed per current block or per sub-block (for example, per 4×4block) in the current block. For example, inter predictor 218 generatesan inter prediction signal of the current block or sub-block by motioncompensation by using motion information (for example, a motion vector)parsed from an encoded bitstream, and outputs the inter predictionsignal to prediction controller 220.

Note that when the information parsed from the encoded bitstreamindicates application of OBMC mode, inter predictor 218 generates theinter prediction signal using motion information for a neighboring blockin addition to motion information for the current block obtained frommotion estimation.

Moreover, when the information parsed from the encoded bitstreamindicates application of FRUC mode, inter predictor 218 derives motioninformation by performing motion estimation in accordance with thepattern matching method (bilateral matching or template matching) parsedfrom the encoded bitstream. Inter predictor 218 then performs motioncompensation using the derived motion information.

Moreover, when BIO mode is to be applied, inter predictor 218 derives amotion vector based on a model assuming uniform linear motion. Moreover,when the information parsed from the encoded bitstream indicates thataffine motion compensation prediction mode is to be applied, interpredictor 218 derives a motion vector of each sub-block based on motionvectors of neighboring blocks.

[Prediction Controller]

Prediction controller 220 selects either the intra prediction signal orthe inter prediction signal, and outputs the selected prediction signalto adder 208.

Embodiment 2

Next, Embodiment 2 is described. In this embodiment, transform andinverse transform are described in detail. It is to be noted that theconfigurations of an encoder and a decoder according to this embodimentare substantially the same as those in Embodiment 1, and are neitherillustrated in the drawings nor described repeatedly.

[Processes Performed by Transformer and Quantizer of Encoder]

First, the processes performed by transformer 106 and quantizer 108 ofencoder 100 according to this embodiment are described specifically withreference to FIG. 11. FIG. 11 is a flow chart illustrating transform andquantization processes in encoder 100 according to Embodiment 2.

First, transformer 106 determines which one of intra prediction andinter prediction is to be used for a current block to be encoded (S101).For example, transformer 106 determines which one of intra predictionand inter prediction is to be used, based on a difference between anoriginal image and a reconstructed image which is obtained by locallydecoding a compressed image and/or a cost based on a coding amount. Inaddition, for example, transformer 106 may determine which one of intraprediction and inter prediction is to be used, based on information (forexample, a picture type) different from the difference and/or the costbased on the coding amount.

Here, when it is determined that inter prediction is to be used for thecurrent block (INTER in S101), transformer 106 selects a first transformbasis for the current block from one or more first transform basiscandidates (S102). For example, transformer 106 fixedly selects a DCT-IItransform basis as a first transform basis for the current block. Inaddition, for example, transformer 106 may select the first transformbasis from a plurality of first transform basis candidates.

Transformer 106 then generates first transform coefficients byperforming first transform of residuals of the current block, using thefirst transform basis selected in Step S102. Quantizer 108 quantizes thegenerated first transform coefficients (S110) to end the transform andquantization processes.

When it is determined that intra prediction is to be used for thecurrent block (INTRA in S101), transformer 106 selects a first transformbasis for the current block from one or more first transform basiscandidates (S104). For example, transformer 106 is capable of selectingthe first transform basis using an adaptive basis selection mode. Theadaptive basis selection mode is a mode for adaptively selecting atransform basis from a plurality of determined transform basiscandidates, based on a difference between an original image and areconstructed image and/or a cost based on a coding amount. Thisadaptive basis selection mode is also referred to as an EMT mode or anAMT mode. As a plurality of transform basis candidates, for example, aplurality of transform bases illustrated in FIG. 6 can be used. It is tobe noted that the plurality of transform basis candidates are notlimited to the plurality of transform bases illustrated in FIG. 6. Theplurality of transform basis candidates may include, for example, atransform basis which is equivalent to not performing transform.

In addition, for example, transformer 106 may select a first transformcoefficient using a non-adaptive basis selection mode (that is, withoutusing the adaptive basis selection mode). In the non-adaptive basisselection mode, for example, transformer 106 is capable of selecting thefirst transform basis based on coding parameters (such as a block size,a quantization parameter, an intra prediction mode, etc.). In addition,transformer 106 is also capable of fixedly selecting a transform basis(for example, a DCT-II transform basis) which has been defined inadvance in a standard, etc. In this case, selecting the transform basismeans fixedly employing one defined transform basis. In addition,transformer 106 may adaptively switch between an adaptive basistransform mode and a non-adaptive basis transform mode.

Transformer 106 then generates first transform coefficients byperforming first transform of the residuals of the current block, usingthe first transform basis selected in Step S104 (S105). Transformer 106determines whether the intra prediction mode for the current block is adetermined mode (S106). For example, transformer 106 determines whetherthe intra prediction mode is the determined mode, based on thedifference between the original image and the reconstructed image and/orthe cost based on the coding amount. It is to be noted that whether theintra prediction mode is the determined mode may be determined based oninformation different from the cost.

The determined mode may be defined in advance in, for example, astandard, etc. In addition, for example, the determined mode may bedetermined based on a coding parameter, etc.

When the intra prediction mode is the determined mode (YES in S106),transformer 106 determines whether the first transform basis selected inStep S104 matches the determined transform basis (S107). The determinedtransform basis may be defined in advance in, for example, a standard,etc. In addition, for example, the determined transform basis may bedetermined based on a coding parameter, etc.

When the intra prediction mode is not the determined mode (NO in S106),or when the first transform basis matches the determined transform basis(YES in S107), transformer 106 selects a second transform basis for thecurrent block from one or more second transform basis candidates (S108).Transformer 106 generates second transform coefficients by performingsecond transform of the first transform coefficients, using the selectedsecond transform basis (S109). Quantizer 108 quantizes the generatedsecond transform coefficients (S110) to end the transform andquantization processes.

In the second transform, secondary transform called NSST may beperformed, or transform in which any of a plurality of second transformbasis candidates is selectively used may be performed. At this time, inthe selection of the second transform basis, a transform basis to beselected may be fixed. In other words, the fixedly determined transformbasis may be selected as the second transform basis. In addition, as thesecond transform basis, a transform basis which is equivalent to notperforming second transform may be used.

When the intra prediction mode is the determined mode (YES in 5106) andthe first transform basis is different from the determined transformbasis (NO in S107), transformer 106 skips the step of selecting a secondtransform basis (S108) and a second transform step (S109). In otherwords, transformer 106 does not perform second transform. In this case,the first transform coefficients generated in Step S105 are quantized(S110) to end the transform and quantization processes.

When the second transform step is skipped in this way, the decoder maybe notified of information indicating that no second transform isperformed. In addition, when the second transform step is skipped,second transform may be performed using a second transform basis whichis equivalent to not performing transform and the decoder may benotified of information indicating the second transform basis.

It is to be noted that inverse quantizer 112 and inverse transformer 114of encoder 100 are capable of reconstructing the current block byperforming the processes inverse to the processes performed bytransformer 106 and quantizer 108.

[Processes Performed by Inverse Quantizer and Inverse Transformer ofDecoder]

Next, the processes performed by inverse quantizer 204 and inversetransformer 206 of decoder 200 according to this embodiment aredescribed specifically with reference to FIG. 12. FIG. 12 is a flowchart illustrating inverse quantization and inverse transform processesin decoder 200 according to Embodiment 2.

First, inverse quantizer 204 inverse quantizes the quantizedcoefficients of a current block to be decoded (S501). Inversetransformer 206 determines which one of intra prediction and interprediction is to be used for the current block (S502). For example,inverse transformer 206 determines which one of intra prediction andinter prediction is to be used, based on information which is obtainedfrom a bitstream.

When it is determined that inter prediction is to be used for thecurrent block (INTER in S502), inverse transformer 206 selects a firstinverse transform basis for the current block (S503). Selecting aninverse transform basis (either a first inverse transform basis or asecond inverse transform basis) in decoder 200 means determining theinverse transform basis based on determined information. As determinedinformation, for example, a basis selection signal can be used.Alternatively, an intra prediction mode, a block size, or the like canbe used as determined information.

Inverse transformer 206 performs first inverse transform of the inversequantized coefficients of the current block, using the first inversetransform basis selected in Step S503 (S504) to end the inversequantization and inverse transform processes.

When it is determined that intra prediction is to be used for thecurrent block (INTRA in S502), inverse transformer 206 determineswhether the intra prediction mode for the current block is a determinedmode (S505). The determined mode which is to be used in decoder 200 isthe same as the determined mode used in encoder 100.

When the intra prediction mode is the determined mode (YES in S505),inverse transformer 206 determines whether the first inverse transformbasis matches a determined inverse transform basis (S506). As thedetermined inverse transform basis, the inverse transform basiscorresponding to the determined transform basis used in encoder 100 isused.

Here, when the intra prediction mode is not the determined mode (NO inS505), or when the first inverse transform basis matches the determinedinverse transform basis (YES in S506), inverse transformer 206 selects asecond inverse transform basis for the current block (S507). Inversetransformer 206 performs second inverse transform of the inversequantized coefficients of the current block, using the selected secondinverse transform basis (S508). Inverse transformer 206 selects a firstinverse transform basis (S509). Inverse transformer 206 performs firstinverse transform of the coefficients obtained through the secondinverse transform in Step S508 (S510) using the selected first inversetransform basis, to end the inverse quantization and inverse transformprocesses.

When the intra prediction mode is the determined mode (YES in 5505) andthe first inverse transform basis is different from the determinedinverse transform basis (NO in S506), inverse transformer 206 skips astep of selecting a second inverse transform (S507) and a second inversetransform step (S508). In other words, inverse transformer 206 selectsthe first inverse transform basis without performing second inversetransform (S509). Inverse transformer 206 performs first inversetransform of the coefficients inverse quantized in Step S501 (S510),using the selected first inverse transform basis (S510) to end theinverse quantization and inverse transform processes.

[Effects, etc.]

The inventors found that a problem of the conventional encoding, thatis, the conventional encoding requires a huge amount of processing forsearching the best combination of a transform basis and a transformparameter (for example, a filter coefficient) in both first transformand second transform. In comparison, encoder 100 and decoder 200according to this embodiment are capable of skipping second transformaccording to an intra prediction mode and a first transform basis. As aresult, it is possible to reduce processing for searching the bestcombination of the transform basis and the transform parameter in boththe first transform and the second transform, thereby reducingprocessing load while reducing decrease in compression efficiency.

Although no second transform is performed when inter prediction is usedfor the current block in this embodiment, it is to be noted that this isa non-limiting example. In other words, when inter prediction is usedfor the current block, second transform of the first transformcoefficients generated by the first transform may be performed. In thiscase, the second transform coefficients generated by the secondtransform are quantized.

It is to be noted that the order of the steps in each of the flow chartsof FIGS. 11 and 12 is not limited to the order in the corresponding oneof FIG. 11 and FIG. 12. For example, in FIG. 11, the step of determiningwhether the intra prediction mode is the determined mode (S106) and thestep of determining whether the first transform basis matches thedetermined transform basis (S107) may be reversed, or may be performedat the same time.

The present aspect may be performed in combination with at least part ofthe other aspects in the present disclosure. In addition, part of theprocessing indicated in any of the flowcharts, part of the configurationof any of the devices, part of syntaxes, etc. according to the presentaspect may be performed in combining with other aspects.

Embodiment 3

Next, Embodiment 3 is described. This embodiment is different fromEmbodiment 2 in that a determined mode to be used for intra predictionmode determination is limited to a non-directional prediction mode. Thisembodiment is described hereinafter mainly focusing on the differencefrom Embodiment 2, with reference to the drawings. It is to be notedthat substantially the same steps as in those in Embodiment 2 areassigned with the same reference marks in each of the drawings, andoverlapping descriptions are skipped or simplified.

[Processes Performed by Transformer and Quantizer of Encoder]

First, the processes performed by transformer 106 and quantizer 108 ofencoder 100 according to this embodiment are described specifically withreference to FIG. 13. FIG. 13 is a flow chart illustrating transform andquantization processes in encoder 100 according to Embodiment 3.

First, transformer 106 determines which one of intra prediction andinter prediction is to be used for a current block to be encoded (S101).Here, when it is determined that inter prediction is to be used for thecurrent block (INTER in S101), transformer 106 selects a first transformbasis (S102), and generates first transform coefficients by performingfirst transform of residuals of the current block, using the selectedfirst transform basis (S103). Quantizer 108 quantizes the generatedfirst transform coefficients (S110) to end the transform andquantization processes.

When it is determined that intra prediction is to be used for thecurrent block (INTRA in S101), transformer 106 determines whether theintra prediction mode for the current block is a non-directionalprediction mode (S201). A non-directional prediction mode is a mode fornot using a specific direction for prediction of a current block to bedecoded. More specifically, the non-directional prediction mode is, forexample, at least one of a DC prediction mode and a Planer predictionmode. In the non-directional prediction mode, for example, pixel valuesare predicted using average values of reference pixels or interpolatedvalues of reference pixels. In contrast, a mode using a specificdirection for prediction of a current block to be decoded is referred toas a directional prediction mode. In the directional prediction mode,pixel values are predicted by extending the values of reference pixelsin a specific direction. It is to be noted that pixel values are thevalues of the pixels included in a picture, and, for example, lumavalues or chroma values.

Here, when the intra prediction mode is different from thenon-directional prediction mode (NO in S201), transformer 106 selects afirst transform basis for the current block (S202). Transformer 106generates first transform coefficients by performing first transform ofthe residuals of the current block, using the first transform basisselected in Step S202. Furthermore, transformer 106 selects a secondtransform basis for the current block (S204). Transformer 106 generatessecond transform coefficients by performing second transform of thefirst transform coefficients generated in Step S203, using the secondtransform basis selected in Step S204 (S205). The processes in Steps5202 to 5205 are substantially the same as the processes in Steps S104to 5109 in the case where the answer in Step S106 is NO in FIG. 11.Subsequently, quantizer 108 quantizes the second transform coefficientsgenerated in Step S205 (5110) to end the transform and quantizationprocesses.

When the intra prediction mode matches the non-directional predictionmode (YES in Step S201), transformer 106 selects the first transformbasis for the current block (S206). Transformer 106 generates firsttransform coefficients by performing first transform of the residuals ofthe current block, using the first transform basis selected in Step S206(S207). Transformer 106 determines whether the first transform basisselected in Step S206 matches a determined transform basis (S208). Asthe determined transform basis, for example, at least one of a DCT-IIand a transform basis similar thereto can be used.

Here, when the first transform basis matches the determined transformbasis (YES in S208), transformer 106 selects a second transform basisfor the current block (S209). Transformer 106 then generates secondtransform coefficients by performing second transform of the firsttransform coefficients generated in Step S207, using the secondtransform basis selected in Step S209 (S210). Subsequently, quantizer108 quantizes the second transform coefficients generated in Step S210(S110) to end the transform and quantization processes.

When the first transform basis is different from the determinedtransform basis (NO in S208), transformer 106 skips a step of selectinga second transform basis (S209) and a second transform step (S210). Inother words, transformer 106 does not perform second transform. In thiscase, the first transform coefficients generated in Step S207 arequantized (S110) to end the transform and quantization processes.

The processes in Steps S206 to S209 are substantially the same as theprocesses in Steps 5104 to 5109 in the case where the answer in StepS106 is YES in FIG. 11.

[Processes Performed by Inverse Quantizer and Inverse Transformer ofDecoder]

Next, the processes performed by inverse quantizer 204 and inversetransformer 206 of decoder 200 according to this embodiment aredescribed specifically with reference to FIG. 14. FIG. 14 is a flowchart illustrating inverse quantization and inverse transform processesin decoder 200 according to Embodiment 3.

First, inverse quantizer 204 inverse quantizes the quantizedcoefficients of a current block to be decoded (S501). Inversetransformer 206 determines which one of intra prediction and interprediction is to be used for the current block (S502).

When it is determined that inter prediction is to be used for thecurrent block (INTER in S502), inverse transformer 206 selects a firstinverse transform basis for the current block (S503). Inversetransformer 206 performs first inverse transform of the inversequantized coefficients of the current block, using the first inversetransform basis selected in Step S503 (S504) to end the inversequantization and inverse transform processes.

When it is determined that intra prediction is to be used for thecurrent block (INTRA in S502), inverse transformer 206 determineswhether the intra prediction mode for the current block is anon-directional prediction mode (S601).

Here, when the intra prediction mode is not the non-directionalprediction mode (NO in S601), inverse quantizer 206 selects a secondinverse transform basis for the current block (S602). Inversetransformer 206 performs second inverse transform of the inversequantized coefficients of the current block, using the selected secondinverse transform basis (S603). Inverse transformer 206 selects a firstinverse transform basis (S604). Inverse transformer 206 performs, usingthe selected first inverse transform basis, first inverse transform ofthe coefficients obtained through the second inverse transform in StepS603 (S605) to end the inverse quantization and inverse transformprocesses.

When the intra prediction mode is the non-directional prediction mode(YES in S601), inverse transformer 206 determines whether the firstinverse transform basis matches a determined inverse transform basis(S606). The determined inverse transform basis to be used in decoder 200is an inverse transform basis corresponding to the determined transformbasis used in encoder 100.

Here, when the first inverse transform basis matches the determinedinverse transform basis (YES in S606), inverse transformer 206 selects asecond inverse transform basis for the current block (S607). Inversetransformer 206 performs second inverse transform of the inversequantized coefficients of the current block, using the selected secondinverse transform basis (S608). Inverse transformer 206 selects a firstinverse transform basis (S609). Inverse transformer 206 performs, usingthe selected first inverse transform basis, first inverse transform ofthe coefficients obtained through the second inverse transform in StepS608 (S610) to end the inverse quantization and inverse transformprocesses.

When the first inverse transform basis is different from the determinedinverse transform basis (NO in S606), inverse transformer 206 skips astep of selecting a second inverse transform basis (S607) and a secondinverse transform step (S608). In other words, inverse transformer 206selects the first inverse transform basis without performing secondinverse transform (S609). Inverse transformer 206 performs first inversetransform of the coefficients inverse quantized in Step S501, using theselected first inverse transform basis (S610) to end the inversequantization and inverse transform processes.

[Effects, etc.]

As described above, encoder 100 and decoder 200 according to thisembodiment makes it possible to skip second transform when the intraprediction mode is the non-directional prediction mode. In thenon-directional prediction mode, residuals are often flat in a block.Accordingly, when a transform basis other than the DCT-II transformbasis and a transform basis similar thereto is used, high-frequencycomponents are likely to remain, and the distribution of transformcoefficients is likely to be random. In this case, the effect ofincreasing compression efficiency by second transform is reduced, andthus, it is possible to reduce processing load while reducing decreasein compression efficiency by skipping the second transform.

Although no second transform is performed when inter prediction is usedfor the current block in this embodiment, it is to be noted that this isa non-limiting example. In other words, when inter prediction is usedfor the current block, second transform of the first transformcoefficients generated by the first transform may be performed. In thiscase, the second transform coefficients generated by the secondtransform are quantized.

It is to be noted that the order of the steps in each of the flow chartsof FIGS. 13 and 14 is not limited to the order in the corresponding oneof FIG. 13 and FIG. 14.

The present aspect may be performed in combination with at least part ofthe other aspects in the present disclosure. In addition, part of theprocessing indicated in any of the flowcharts, part of the configurationof any of the devices, part of syntaxes, etc. according to the presentaspect may be performed in combining with other aspects.

Embodiment 4

Next, Embodiment 4 is described. This embodiment is different fromEmbodiment 2 in that a first transform basis is fixed according to ablock size in an adaptive basis selection mode. This embodiment isdescribed hereinafter mainly focusing on the differences fromEmbodiments 2 and 3, with reference to the drawings. It is to be notedthat substantially the same steps as in those in Embodiments 2 and 3 areassigned with the same reference marks in each of the drawings, andoverlapping descriptions are skipped or simplified.

[Processes Performed by Transformer and Quantizer of Encoder]

First, the processes performed by transformer 106 and quantizer 108 ofencoder 100 according to this embodiment are described specifically withreference to FIG. 15. FIG. 15 is a flow chart illustrating transform andquantization processes in encoder 100 according to Embodiment 4.

First, transformer 106 determines which one of intra prediction andinter prediction is to be used for a current block to be encoded (S101).Here, when it is determined that inter prediction is to be used for thecurrent block (INTER in S101), transformer 106 selects a first transformbasis (S102), and generates first transform coefficients by performingfirst transform of residuals of the current block using the selectedfirst transform basis (S103). Quantizer 108 quantizes the generatedfirst transform coefficients (S110) to end the transform andquantization processes.

When it is determined that intra prediction is to be used for thecurrent block (INTRA in S101), transformer 106 determines whether thesize of the current block matches a determined size, and whether theadaptive basis selection mode is to be used for the current block(S301). Whether to use the adaptive basis selection mode can bedetermined based on a difference between an original image and areconstructed image and/or a cost based on a coding amount.

As the determined size, for example, a specific block size defined inadvance in a standard, etc. can be used. More specifically, for example,4×4 pixels can be used as the predetermined size. Alternatively, aplurality of block sizes may be used as determined sizes. Morespecifically, for example, 4×4 pixels, 8×4 pixels, and 4×8 pixels may beused as determined sizes. In addition, whether the size of a currentblock to be encoded matches a determined size may be determined bydetermining whether the size of the current block satisfies a determinedcondition. In this case, the determined condition is, for example, botha horizontal size and a vertical size are smaller than a determinednumber of pixels, or at least one of the horizontal size and thevertical size is smaller than the determined number of pixels.

When the size of the current block is different from the determinedsize, or when the adaptive basis selection mode is not to be used (NO inS301), transformer 106 determines whether the intra prediction mode forthe current block is a non-directional prediction mode (S201).

Here, when the intra prediction mode is different from thenon-directional prediction mode (NO in S201), transformer 106 selects afirst transform basis for the current block (S202). For example, when itis determined that the adaptive basis selection mode is to be used,transformer 106 adaptively selects a first transform basis from aplurality of first transform basis candidates. In addition, for example,when it is determined that the adaptive basis selection mode is not tobe used, transformer 106 fixedly selects a defined transform basis (forexample, a DCT-II transform basis).

Transformer 106 generates first transform coefficients by performingfirst transform of the residuals of the current block, using the firsttransform basis selected in Step S202 (S203). Furthermore, transformer106 selects a second transform basis for the current block (S204).Transformer 106 generates second transform coefficients by performingsecond transform of the first transform coefficients generated in StepS203, using the second transform basis selected in Step S204 (S205).Subsequently, quantizer 108 quantizes the second transform coefficientsgenerated in Step S205 (S110) to end the transform and quantizationprocesses.

When the intra prediction mode matches the non-directional predictionmode (YES in Step S201), transformer 106 selects a first transform basisfor the current block (S206). For example, when it is determined thatthe adaptive basis selection mode is to be used, transformer 106adaptively selects a first transform basis from a plurality of firsttransform basis candidates. In addition, for example, when it isdetermined that the adaptive basis selection mode is not to be used,transformer 106 fixedly selects a defined transform basis (for example,a DCT-II transform basis).

Transformer 106 generates first transform coefficients by performingfirst transform of residuals of the current block, using the firsttransform basis selected in Step S206 (S207). Transformer 106 determineswhether the first transform basis selected in Step S206 matches a seconddetermined transform basis (S208). As the second determined transformbasis, for example, at least one of a DCT-II transform basis and atransform basis similar thereto can be used.

Here, when the first transform basis matches the second determinedtransform basis (YES in S208), transformer 106 selects a secondtransform basis for the current block (S209). Transformer 106 thengenerates second transform coefficients by performing second transformof the first transform coefficients generated in Step S207, using thesecond transform basis selected in Step S209 (S210). Subsequently,quantizer 108 quantizes the second transform coefficients generated inStep S210 (S110) to end the transform and quantization processes.

When the first transform basis is different from the second determinedtransform basis (NO in S208), transformer 106 skips a step of selectinga second transform basis (S209) and a second transform step (S210). Inother words, transformer 106 does not perform second transform. In thiscase, the first transform coefficients generated in Step S207 arequantized (S110) to end the transform and quantization processes.

When the size of the current block matches the determined size and theadaptive basis selection mode is to be used (YES in S301), transformer106 fixes the first transform basis to the first determined transformbasis (S302). As the first determined transform basis, for example, aDST-VII transform basis can be used. It is to be noted that the firstdetermined transform basis is not limited to the DST-VII transformbasis. For example, as the first determined transform basis, a DCT-Vtransform basis may be used.

Transformer 106 generates first transform coefficients by performingfirst transform of the residuals of the current block, using the firsttransform basis fixed in Step S302 (S303). Transformer 106 determineswhether the intra prediction mode for the current block is anon-directional prediction mode (S304).

Here, when the intra prediction mode is different from thenon-directional prediction mode (NO in S304), transformer 106 selects asecond transform basis (S305). Transformer 106 then generates secondtransform coefficients by performing second transform of the firsttransform coefficients generated in Step S303, using the secondtransform basis selected in Step S305 (S306). Subsequently, quantizer108 quantizes the second transform coefficients generated in Step S306(S110) to end the transform and quantization processes.

When the intra prediction mode matches the non-directional predictionmode (YES in S304), transformer 106 skips the step of selecting a secondtransform basis (S305) and a second transform step (S306). In otherwords, transformer 106 does not perform second transform. In this case,the first transform coefficients generated in Step S303 are quantized(S110) to end the transform and quantization processes.

[Processes Performed by Entropy Encoder of Encoder]

Next, an encoding process related to transform by entropy encoder 110 ofencoder 100 according to this embodiment is described specifically withreference to FIG. 16. FIG. 16 is a flow chart illustrating the encodingprocess in encoder 100 according to Embodiment 4.

When inter prediction has been used for a current block to be encoded(INTER in S401), entropy encoder 110 encodes a first basis selectionsignal in a bitstream (S402). Here, the first basis selection signal isinformation or data indicating the first transform basis selected inStep S102.

Encoding the signal in the bitstream means disposing a code indicatingthe information in the bitstream. The code is, for example, generated bycontext adaptive binary arithmetic coding (CABAC). It is to be notedthat CABAC does not always need to be used to generate a code, andentropy encoding does not always need to be used. For example, the codemay be information itself (for example, a flag indicating 0 or 1).

Next, entropy encoder 110 encodes the coefficients quantized in StepS110 (S403) to end the encoding process.

When intra prediction is used for the current block (INTRA in S401),entropy encoder 110 encodes an intra prediction mode signal indicatingan intra prediction mode for the current block in the bitstream (S404).Furthermore, entropy encoder 110 encodes, in the bitstream, an adaptiveselection mode signal indicating whether the adaptive basis selectionmode has been used for the current block (S405).

Here, when the adaptive basis selection mode has been used and the sizeof the current block is different from a determined size (YES in S406),entropy encoder 110 encodes a first basis selection signal in thebitstream (S407). Here, the first basis selection signal is informationor data indicating the first transform basis selected in Step S202 orS206. When the adaptive basis selection mode has not been used, or whenthe adaptive basis selection mode has been used and the size of thecurrent block matches the determined size (NO in S406), entropy encoder110 skips the step of encoding the first basis selection signal (S407).In other words, entropy encoder 110 does not encode the first basisselection signal.

Here, when second transform is performed (YES in S408), entropy encoder110 encodes a second transform selection signal in the bitstream (S409).Here, the second basis selection signal is information or dataindicating the second transform basis selected in Step S204, S209, orS305. When no second transform has been performed (NO in S408), entropyencoder 110 skips the step of encoding the second basis selection signal(S409). In other words, entropy encoder 110 does not encode the secondbasis selection signal.

Lastly, entropy encoder 110 encodes the coefficients quantized in StepS110 (S410) to end the encoding process.

[Process Performed by Entropy Decoder of Decoder]

Next, the process performed by entropy decoder 202 of decoder 200according to this embodiment is described specifically with reference toFIG. 17. FIG. 17 is a flow chart illustrating decoding processes indecoder 200 according to Embodiment 4.

When inter prediction is used for a current block to be decoded (INTERin S701), entropy decoder 202 decodes the first basis selection signalfrom the bitstream (S702).

Decoding the signal from the bitstream means parsing the code indicatingthe information from the bitstream and restore the information from theparsed code. For example, context adaptive binary arithmetic decoding(CABAD) is used to restore the information from the code. It is to benoted that CABAD does not always need to be used to restore informationfrom a code, and entropy decoding does not always need to be used. Forexample, when the parsed code itself indicates information (for example,a flag indicating 0 or 1), it is only necessary that the code is simplyparsed.

Next, entropy decoder 202 decodes quantized coefficients from thebitstream (S703) to end the decoding process.

When intra prediction is to be used for the current block (INTRA inS701), entropy decoder 202 decodes the intra prediction mode signal fromthe bitstream (S704). Furthermore, entropy decoder 202 decodes theadaptive selection mode signal (S705).

Here, when the adaptive basis selection mode is used and the size of thecurrent block is different from a determined size (YES in S706), entropydecoder 202 decodes the first basis selection signal from the bitstream(S707). When the adaptive basis selection mode has not been used, orwhen the adaptive basis selection mode is used and the size of thecurrent block matches the determined size (NO in S706), entropy decoder202 skips the step of decoding the first basis selection signal (S707).In other words, entropy decoder 202 does not decode the first basisselection signal.

Here, when second inverse transform is to be performed (YES in S708),entropy decoder 202 decodes the second basis selection signal from thebitstream (S709). When no second inverse transform is to be performed(NO in S708), entropy decoder 202 skips the step of decoding the secondbasis selection signal (S709). In other words, entropy decoder 202 doesnot decode the second basis selection signal.

Lastly, entropy decoder 202 decodes quantized coefficients from thebitstream (S710) to end the decoding process.

[Processes Performed by Inverse Quantizer and Inverse Transformer ofDecoder]

Next, the processes performed by inverse quantizer 204 and inversetransformer 206 of decoder 200 according to this embodiment aredescribed specifically with reference to FIG. 18. FIG. 18 is a flowchart illustrating inverse quantization and inverse transform processesin decoder 200 according to Embodiment 4.

First, inverse quantizer 204 inverse quantizes the quantizedcoefficients of a current block to be decoded (S501). Inversetransformer 206 determines which one of intra prediction and interprediction is to be used for the current block (S502). When it isdetermined that inter prediction is to be used for the current block(INTER in S502), inverse transformer 206 selects a first inversetransform basis for the current block (S503). Inverse transformer 206performs first inverse transform of the inverse quantized coefficientsof the current block, using the first inverse transform basis selectedin Step S503 (S504) to end the inverse quantization and inversetransform processes.

When it is determined that intra prediction is to be used for thecurrent block (INTRA in S502), inverse transformer 206 determineswhether the size of the current block matches a determined size andwhether an adaptive basis selection mode has been used for the currentblock (S801). For example, inverse transformer 206 determines whetherthe adaptive basis selection mode has been used, based on the adaptiveselection mode signal decoded in Step S705 in FIG. 17.

When the size of the current block is different from the determinedsize, or when the adaptive basis selection mode has not been used (NO inS801), inverse transformer 206 determines whether the intra predictionmode for the current block is a non-directional prediction mode (S601).

Here, when the intra prediction mode is not the non-directionalprediction mode (NO in S601), inverse quantizer 206 selects a secondinverse transform basis for the current block (S602). For example,inverse transformer 206 selects a second inverse transform basis, basedon the second basis selection signal decoded in Step S709 in FIG. 17.Inverse transformer 206 performs second inverse transform of the inversequantized coefficients of the current block, using the selected secondinverse transform basis (S603). Inverse transformer 206 selects a firstinverse transform basis (S604). For example, when the adaptive basisselection mode has been used, inverse transformer 206 selects a firstinverse transform basis, based on the first basis selection signaldecoded in Step S707 in FIG. 17. Inverse transformer 206 performs firstinverse transform of the coefficients obtained through the secondinverse transform in Step S603 (S605) to end the inverse quantizationand inverse transform processes.

When the intra prediction mode is the non-directional prediction mode(YES in S601), inverse transformer 206 determines whether the firstinverse transform basis matches a second determined inverse transformbasis (S606). For example, when the adaptive basis selection mode hasbeen used, inverse transformer 206 determines whether the first inversetransform basis matches the second determined inverse transform basis,based on the first basis selection signal decoded in Step S707 in FIG.17. As the second determined inverse transform basis, the inversetransform basis corresponding to the second determined transform basisused in encoder 100 is used.

Here, when the first inverse transform basis matches the seconddetermined inverse transform basis (YES in S606), inverse transformer206 selects a second inverse transform basis for the current block(S607). For example, inverse transformer 206 selects a second inversetransform basis, based on the second basis selection signal decoded inStep S709 in FIG. 17. Inverse transformer 206 performs second inversetransform of the inverse quantized coefficients of the current block,using the selected second inverse transform basis (S608). Inversetransformer 206 selects a first inverse transform basis (S609). Forexample, when the adaptive basis selection mode has been used, inversetransformer 206 selects a first inverse transform basis, based on thefirst basis selection signal decoded in Step S707 in FIG. 17. Inversetransformer 206 performs first inverse transform of the coefficientsobtained through the second inverse transform in Step S608 (S610) usingthe selected first inverse transform basis, to end the inversequantization and inverse transform processes.

When the size of the current block matches the determined size and theadaptive basis selection mode has been used (YES in S801), inversetransformer 206 determines whether the intra prediction mode for thecurrent block is the non-directional prediction mode (S802).

Here, when the intra prediction mode is not the non-directionalprediction mode (NO in S802), inverse transformer 206 selects a secondinverse transform basis for the current block (S803). For example,inverse transformer 206 selects a second inverse transform basis, basedon the second basis selection signal decoded in Step S709 in FIG. 17.Inverse transformer 206 performs second inverse transform of the inversequantized coefficients of the current block, using the selected secondinverse transform basis (S804). Inverse transformer 206 fixes a firstinverse transform basis to a first determined inverse transform basis(S805). As the first determined inverse transform basis, the inversetransform basis corresponding to the first determined transform basisused in encoder 100 is used. Inverse transformer 206 performs firstinverse transform of the coefficients obtained through the secondinverse transform in Step S804 (S806) using the selected first inversetransform basis, to end the inverse quantization and inverse transformprocesses.

When the intra prediction mode is the non-directional prediction mode(YES in S802), inverse transformer 206 skips the step of selecting asecond inverse transform basis (S803) and a second inverse transformstep (S804). In other words, inverse transformer 206 fixes the firstinverse transform basis to a first determined inverse transform basiswithout performing second inverse transform (S805). Inverse transformer206 performs first inverse transform of the coefficients inversequantized in Step S501, using the fixed first inverse transform basis(S806) to end the inverse quantization and inverse transform processes.

[Effects, etc.]

As described above, encoder 100 and decoder 200 according to thisembodiment are capable of fixing a first transform basis according to ablock size when an adaptive basis selection mode is used. Accordingly,it is possible to reduce the load for first transform in the adaptivebasis selection mode.

Although no second transform is performed when inter prediction is usedfor the current block in this embodiment, it is to be noted that this isa non-limiting example. In other words, when inter prediction is usedfor the current block, second transform of the first transformcoefficients generated by the first transform may be performed. In thiscase, the second transform coefficients generated by the secondtransform are quantized.

It is to be noted that the order of the steps in each of the flow chartsof FIGS. 15 to 18 is not limited to the order in the corresponding oneof FIG. 15 to FIG. 18. For example, in FIG. 16, the signal coding ordermay be another order defined in advance in a standard, etc.

Although the plurality of signals (the intra prediction mode signal, theadaptive selection mode signal, the first basis selection signal, andthe second basis selection signal) are encoded in the bistream in thisembodiment, it is to be noted that the plurality of signals do notalways need to be encoded in the bitstream. For example, decoder 200 maybe notified of the plurality of signals by encoder 100, separately fromthe bitstream.

It is to be noted that the positions of the plurality of signals (theintra prediction mode signal, the adaptive selection mode signal, thefirst basis selection signal, and the second basis selection signal) inthe bitstream are not particularly limited. The plurality of signalsare, for example, encoded in at least one of a plurality of headers. Asthe plurality of headers, for example, a video parameter set, a sequenceparameter et, a picture parameter set, and a slice header can be used.It is to be noted that, when a signal is present in a plurality ofhierarchical layers (for example, a picture parameter set and a sliceheader), the signal present in the lower hierarchical layer (forexample, the slice header) overwrites the signal present in the higherhierarchical layer (for example, the picture parameter set).

The present aspect may be performed in combination with at least part ofthe other aspects in the present disclosure. In addition, part of theprocessing indicated in any of the flowcharts, part of the configurationof any of the devices, part of syntaxes, etc. according to the presentaspect may be performed in combining with other aspects.

Embodiment 5

As described in each of the above embodiments and variations, eachfunctional block can typically be realized as an MPU and memory, forexample. Moreover, processes performed by each of the functional blocksare typically realized by a program execution unit, such as a processor,reading and executing software (a program) recorded on a recordingmedium such as ROM. The software may be distributed via, for example,downloading, and may be recorded on a recording medium such assemiconductor memory and distributed. Note that each functional blockcan, of course, also be realized as hardware (dedicated circuit).

Moreover, the processing described in each of the embodiments andvariations may be realized via integrated processing using a singleapparatus (system), and, alternatively, may be realized viadecentralized processing using a plurality of apparatuses. Moreover, theprocessor that executes the above-described program may be a singleprocessor or a plurality of processors. In other words, integratedprocessing may be performed, and, alternatively, decentralizedprocessing may be performed.

Embodiments of the present invention are not limited to the aboveexemplary embodiments; various modifications may be made to theexemplary embodiments, the results of which are also included within thescope of the embodiments of the present invention.

Next, application examples of the moving picture encoding method (imageencoding method) and the moving picture decoding method (image decodingmethod) described in each of the above embodiments and variations and asystem that employs the same will be described. The system ischaracterized as including an image encoder that employs the imageencoding method, an image decoder that employs the image decodingmethod, and an image encoder/decoder that includes both the imageencoder and the image decoder. Other configurations included in thesystem may be modified on a case-by-case basis.

[Usage Examples]

FIG. 19 illustrates an overall configuration of content providing systemex100 for implementing a content distribution service. The area in whichthe communication service is provided is divided into cells of desiredsizes, and base stations ex106, ex107, ex108, ex109, and ex110, whichare fixed wireless stations, are located in respective cells.

In content providing system ex100, devices including computer ex111,gaming device ex112, camera ex113, home appliance ex114, and smartphoneex115 are connected to internet ex101 via internet service providerex102 or communications network ex104 and base stations ex106 throughex110. Content providing system ex100 may combine and connect anycombination of the above elements. The devices may be directly orindirectly connected together via a telephone network or near fieldcommunication rather than via base stations ex106 through ex110, whichare fixed wireless stations. Moreover, streaming server ex103 isconnected to devices including computer ex111, gaming device ex112,camera ex113, home appliance ex114, and smartphone ex115 via, forexample, internet ex101. Streaming server ex103 is also connected to,for example, a terminal in a hotspot in airplane ex117 via satelliteex116.

Note that instead of base stations ex106 through ex110, wireless accesspoints or hotspots may be used. Streaming server ex103 may be connectedto communications network ex104 directly instead of via internet ex101or internet service provider ex102, and may be connected to airplaneex117 directly instead of via satellite ex116.

Camera ex113 is a device capable of capturing still images and video,such as a digital camera. Smartphone ex115 is a smartphone device,cellular phone, or personal handyphone system (PHS) phone that canoperate under the mobile communications system standards of the typical2G, 3G, 3.9G, and 4G systems, as well as the next-generation 5G system.

Home appliance ex118 is, for example, a refrigerator or a deviceincluded in a home fuel cell cogeneration system.

In content providing system ex100, a terminal including an image and/orvideo capturing function is capable of, for example, live streaming byconnecting to streaming server ex103 via, for example, base stationex106. When live streaming, a terminal (e.g., computer ex111, gamingdevice ex112, camera ex113, home appliance ex114, smartphone ex115, orairplane ex117) performs the encoding processing described in the aboveembodiments and variations on still-image or video content captured by auser via the terminal, multiplexes video data obtained via the encodingand audio data obtained by encoding audio corresponding to the video,and transmits the obtained data to streaming server ex103. In otherwords, the terminal functions as the image encoder according to oneaspect of the present invention.

Streaming server ex103 streams transmitted content data to clients thatrequest the stream. Client examples include computer ex111, gamingdevice ex112, camera ex113, home appliance ex114, smartphone ex115, andterminals inside airplane ex117, which are capable of decoding theabove-described encoded data. Devices that receive the streamed datadecode and reproduce the received data. In other words, the devices eachfunction as the image decoder according to one aspect of the presentinvention.

[Decentralized Processing]

Streaming server ex103 may be realized as a plurality of servers orcomputers between which tasks such as the processing, recording, andstreaming of data are divided. For example, streaming server ex103 maybe realized as a content delivery network (CDN) that streams content viaa network connecting multiple edge servers located throughout the world.In a CDN, an edge server physically near the client is dynamicallyassigned to the client. Content is cached and streamed to the edgeserver to reduce load times. In the event of, for example, some kind ofan error or a change in connectivity due to, for example, a spike intraffic, it is possible to stream data stably at high speeds since it ispossible to avoid affected parts of the network by, for example,dividing the processing between a plurality of edge servers or switchingthe streaming duties to a different edge server, and continuingstreaming.

Decentralization is not limited to just the division of processing forstreaming; the encoding of the captured data may be divided between andperformed by the terminals, on the server side, or both. In one example,in typical encoding, the processing is performed in two loops. The firstloop is for detecting how complicated the image is on a frame-by-frameor scene-by-scene basis, or detecting the encoding load. The second loopis for processing that maintains image quality and improves encodingefficiency. For example, it is possible to reduce the processing load ofthe terminals and improve the quality and encoding efficiency of thecontent by having the terminals perform the first loop of the encodingand having the server side that received the content perform the secondloop of the encoding. In such a case, upon receipt of a decodingrequest, it is possible for the encoded data resulting from the firstloop performed by one terminal to be received and reproduced on anotherterminal in approximately real time. This makes it possible to realizesmooth, real-time streaming.

In another example, camera ex113 or the like extracts a feature amountfrom an image, compresses data related to the feature amount asmetadata, and transmits the compressed metadata to a server. Forexample, the server determines the significance of an object based onthe feature amount and changes the quantization accuracy accordingly toperform compression suitable for the meaning of the image. Featureamount data is particularly effective in improving the precision andefficiency of motion vector prediction during the second compressionpass performed by the server. Moreover, encoding that has a relativelylow processing load, such as variable length coding (VLC), may behandled by the terminal, and encoding that has a relatively highprocessing load, such as context-adaptive binary arithmetic coding(CABAC), may be handled by the server.

In yet another example, there are instances in which a plurality ofvideos of approximately the same scene are captured by a plurality ofterminals in, for example, a stadium, shopping mall, or factory. In sucha case, for example, the encoding may be decentralized by dividingprocessing tasks between the plurality of terminals that captured thevideos and, if necessary, other terminals that did not capture thevideos and the server, on a per-unit basis. The units may be, forexample, groups of pictures (GOP), pictures, or tiles resulting fromdividing a picture. This makes it possible to reduce load times andachieve streaming that is closer to real-time.

Moreover, since the videos are of approximately the same scene,management and/or instruction may be carried out by the server so thatthe videos captured by the terminals can be cross-referenced. Moreover,the server may receive encoded data from the terminals, change referencerelationship between items of data or correct or replace picturesthemselves, and then perform the encoding. This makes it possible togenerate a stream with increased quality and efficiency for theindividual items of data.

Moreover, the server may stream video data after performing transcodingto convert the encoding format of the video data. For example, theserver may convert the encoding format from MPEG to VP, and may convertH.264 to H.265.

In this way, encoding can be performed by a terminal or one or moreservers. Accordingly, although the device that performs the encoding isreferred to as a “server” or “terminal” in the following description,some or all of the processes performed by the server may be performed bythe terminal, and likewise some or all of the processes performed by theterminal may be performed by the server. This also applies to decodingprocesses.

[3D, Multi-angle]

In recent years, usage of images or videos combined from images orvideos of different scenes concurrently captured or the same scenecaptured from different angles by a plurality of terminals such ascamera ex113 and/or smartphone ex115 has increased. Videos captured bythe terminals are combined based on, for example, theseparately-obtained relative positional relationship between theterminals, or regions in a video having matching feature points.

In addition to the encoding of two-dimensional moving pictures, theserver may encode a still image based on scene analysis of a movingpicture either automatically or at a point in time specified by theuser, and transmit the encoded still image to a reception terminal.Furthermore, when the server can obtain the relative positionalrelationship between the video capturing terminals, in addition totwo-dimensional moving pictures, the server can generatethree-dimensional geometry of a scene based on video of the same scenecaptured from different angles. Note that the server may separatelyencode three-dimensional data generated from, for example, a pointcloud, and may, based on a result of recognizing or tracking a person orobject using three-dimensional data, select or reconstruct and generatea video to be transmitted to a reception terminal from videos capturedby a plurality of terminals.

This allows the user to enjoy a scene by freely selecting videoscorresponding to the video capturing terminals, and allows the user toenjoy the content obtained by extracting, from three-dimensional datareconstructed from a plurality of images or videos, a video from aselected viewpoint. Furthermore, similar to with video, sound may berecorded from relatively different angles, and the server may multiplex,with the video, audio from a specific angle or space in accordance withthe video, and transmit the result.

In recent years, content that is a composite of the real world and avirtual world, such as virtual reality (VR) and augmented reality (AR)content, has also become popular. In the case of VR images, the servermay create images from the viewpoints of both the left and right eyesand perform encoding that tolerates reference between the two viewpointimages, such as multi-view coding (MVC), and, alternatively, may encodethe images as separate streams without referencing. When the images aredecoded as separate streams, the streams may be synchronized whenreproduced so as to recreate a virtual three-dimensional space inaccordance with the viewpoint of the user.

In the case of AR images, the server superimposes virtual objectinformation existing in a virtual space onto camera informationrepresenting a real-world space, based on a three-dimensional positionor movement from the perspective of the user. The decoder may obtain orstore virtual object information and three-dimensional data, generatetwo-dimensional images based on movement from the perspective of theuser, and then generate superimposed data by seamlessly connecting theimages. Alternatively, the decoder may transmit, to the server, motionfrom the perspective of the user in addition to a request for virtualobject information, and the server may generate superimposed data basedon three-dimensional data stored in the server in accordance with thereceived motion, and encode and stream the generated superimposed datato the decoder. Note that superimposed data includes, in addition to RGBvalues, an a value indicating transparency, and the server sets the avalue for sections other than the object generated fromthree-dimensional data to, for example, 0, and may perform the encodingwhile those sections are transparent. Alternatively, the server may setthe background to a predetermined RGB value, such as a chroma key, andgenerate data in which areas other than the object are set as thebackground.

Decoding of similarly streamed data may be performed by the client(i.e., the terminals), on the server side, or divided therebetween. Inone example, one terminal may transmit a reception request to a server,the requested content may be received and decoded by another terminal,and a decoded signal may be transmitted to a device having a display. Itis possible to reproduce high image quality data by decentralizingprocessing and appropriately selecting content regardless of theprocessing ability of the communications terminal itself. In yet anotherexample, while a TV, for example, is receiving image data that is largein size, a region of a picture, such as a tile obtained by dividing thepicture, may be decoded and displayed on a personal terminal orterminals of a viewer or viewers of the TV. This makes it possible forthe viewers to share a big-picture view as well as for each viewer tocheck his or her assigned area or inspect a region in further detail upclose.

In the future, both indoors and outdoors, in situations in which aplurality of wireless connections are possible over near, mid, and fardistances, it is expected to be able to seamlessly receive content evenwhen switching to data appropriate for the current connection, using astreaming system standard such as MPEG-DASH. With this, the user canswitch between data in real time while freely selecting a decoder ordisplay apparatus including not only his or her own terminal, but also,for example, displays disposed indoors or outdoors. Moreover, based on,for example, information on the position of the user, decoding can beperformed while switching which terminal handles decoding and whichterminal handles the displaying of content. This makes it possible to,while in route to a destination, display, on the wall of a nearbybuilding in which a device capable of displaying content is embedded oron part of the ground, map information while on the move. Moreover, itis also possible to switch the bit rate of the received data based onthe accessibility to the encoded data on a network, such as when encodeddata is cached on a server quickly accessible from the receptionterminal or when encoded data is copied to an edge server in a contentdelivery service.

[Scalable Encoding]

The switching of content will be described with reference to a scalablestream, illustrated in FIG. 20, that is compression coded viaimplementation of the moving picture encoding method described in theabove embodiments and variations. The server may have a configuration inwhich content is switched while making use of the temporal and/orspatial scalability of a stream, which is achieved by division into andencoding of layers, as illustrated in FIG. 118. Note that there may be aplurality of individual streams that are of the same content butdifferent quality. In other words, by determining which layer to decodeup to based on internal factors, such as the processing ability on thedecoder side, and external factors, such as communication bandwidth, thedecoder side can freely switch between low resolution content and highresolution content while decoding. For example, in a case in which theuser wants to continue watching, at home on a device such as a TVconnected to the internet, a video that he or she had been previouslywatching on smartphone ex115 while on the move, the device can simplydecode the same stream up to a different layer, which reduces serverside load.

Furthermore, in addition to the configuration described above in whichscalability is achieved as a result of the pictures being encoded perlayer and the enhancement layer is above the base layer, the enhancementlayer may include metadata based on, for example, statisticalinformation on the image, and the decoder side may generate high imagequality content by performing super-resolution imaging on a picture inthe base layer based on the metadata. Super-resolution imaging may beimproving the SN ratio while maintaining resolution and/or increasingresolution. Metadata includes information for identifying a linear or anon-linear filter coefficient used in super-resolution processing, orinformation identifying a parameter value in filter processing, machinelearning, or least squares method used in super-resolution processing.

Alternatively, a configuration in which a picture is divided into, forexample, tiles in accordance with the meaning of, for example, an objectin the image, and on the decoder side, only a partial region is decodedby selecting a tile to decode, is also acceptable. Moreover, by storingan attribute about the object (person, car, ball, etc.) and a positionof the object in the video (coordinates in identical images) asmetadata, the decoder side can identify the position of a desired objectbased on the metadata and determine which tile or tiles include thatobject. For example, as illustrated in FIG. 21, metadata is stored usinga data storage structure different from pixel data such as an SEImessage in HEVC. This metadata indicates, for example, the position,size, or color of the main object.

Moreover, metadata may be stored in units of a plurality of pictures,such as stream, sequence, or random access units. With this, the decoderside can obtain, for example, the time at which a specific personappears in the video, and by fitting that with picture unit information,can identify a picture in which the object is present and the positionof the object in the picture.

[Web Page Optimization]

FIG. 22 illustrates an example of a display screen of a web page on, forexample, computer ex111. FIG. 23 illustrates an example of a displayscreen of a web page on, for example, smartphone ex115. As illustratedin FIG. 22 and FIG. 23, a web page may include a plurality of imagelinks which are links to image content, and the appearance of the webpage differs depending on the device used to view the web page. When aplurality of image links are viewable on the screen, until the userexplicitly selects an image link, or until the image link is in theapproximate center of the screen or the entire image link fits in thescreen, the display apparatus (decoder) displays, as the image links,still images included in the content or I pictures, displays video suchas an animated gif using a plurality of still images or I pictures, forexample, or receives only the base layer and decodes and displays thevideo.

When an image link is selected by the user, the display apparatusdecodes giving the highest priority to the base layer. Note that ifthere is information in the HTML code of the web page indicating thatthe content is scalable, the display apparatus may decode up to theenhancement layer. Moreover, in order to guarantee real timereproduction, before a selection is made or when the bandwidth isseverely limited, the display apparatus can reduce delay between thepoint in time at which the leading picture is decoded and the point intime at which the decoded picture is displayed (that is, the delaybetween the start of the decoding of the content to the displaying ofthe content) by decoding and displaying only forward reference pictures(I picture, P picture, forward reference B picture). Moreover, thedisplay apparatus may purposely ignore the reference relationshipbetween pictures and coarsely decode all B and P pictures as forwardreference pictures, and then perform normal decoding as the number ofpictures received over time increases.

[Autonomous Driving]

When transmitting and receiving still image or video data such two- orthree-dimensional map information for autonomous driving or assisteddriving of an automobile, the reception terminal may receive, inaddition to image data belonging to one or more layers, information on,for example, the weather or road construction as metadata, and associatethe metadata with the image data upon decoding. Note that metadata maybe assigned per layer and, alternatively, may simply be multiplexed withthe image data.

In such a case, since the automobile, drone, airplane, etc., includingthe reception terminal is mobile, the reception terminal can seamlesslyreceive and decode while switching between base stations among basestations ex106 through ex110 by transmitting information indicating theposition of the reception terminal upon reception request. Moreover, inaccordance with the selection made by the user, the situation of theuser, or the bandwidth of the connection, the reception terminal candynamically select to what extent the metadata is received or to whatextent the map information, for example, is updated.

With this, in content providing system ex100, the client can receive,decode, and reproduce, in real time, encoded information transmitted bythe user.

[Streaming of Individual Content]

In content providing system ex100, in addition to high image quality,long content distributed by a video distribution entity, unicast ormulticast streaming of low image quality, short content from anindividual is also possible. Moreover, such content from individuals islikely to further increase in popularity. The server may first performediting processing on the content before the encoding processing inorder to refine the individual content. This may be achieved with, forexample, the following configuration.

In real-time while capturing video or image content or after the contenthas been captured and accumulated, the server performs recognitionprocessing based on the raw or encoded data, such as capture errorprocessing, scene search processing, meaning analysis, and/or objectdetection processing. Then, based on the result of the recognitionprocessing, the server—either when prompted or automatically—edits thecontent, examples of which include: correction such as focus and/ormotion blur correction; removing low-priority scenes such as scenes thatare low in brightness compared to other pictures or out of focus; objectedge adjustment; and color tone adjustment. The server encodes theedited data based on the result of the editing. It is known thatexcessively long videos tend to receive fewer views. Accordingly, inorder to keep the content within a specific length that scales with thelength of the original video, the server may, in addition to thelow-priority scenes described above, automatically clip out scenes withlow movement based on an image processing result. Alternatively, theserver may generate and encode a video digest based on a result of ananalysis of the meaning of a scene.

Note that there are instances in which individual content may includecontent that infringes a copyright, moral right, portrait rights, etc.Such an instance may lead to an unfavorable situation for the creator,such as when content is shared beyond the scope intended by the creator.Accordingly, before encoding, the server may, for example, edit imagesso as to blur faces of people in the periphery of the screen or blur theinside of a house, for example. Moreover, the server may be configuredto recognize the faces of people other than a registered person inimages to be encoded, and when such faces appear in an image, forexample, apply a mosaic filter to the face of the person. Alternatively,as pre- or post-processing for encoding, the user may specify, forcopyright reasons, a region of an image including a person or a regionof the background be processed, and the server may process the specifiedregion by, for example, replacing the region with a different image orblurring the region. If the region includes a person, the person may betracked in the moving picture, and the head region may be replaced withanother image as the person moves.

Moreover, since there is a demand for real-time viewing of contentproduced by individuals, which tends to be small in data size, thedecoder first receives the base layer as the highest priority andperforms decoding and reproduction, although this may differ dependingon bandwidth. When the content is reproduced two or more times, such aswhen the decoder receives the enhancement layer during decoding andreproduction of the base layer and loops the reproduction, the decodermay reproduce a high image quality video including the enhancementlayer. If the stream is encoded using such scalable encoding, the videomay be low quality when in an unselected state or at the start of thevideo, but it can offer an experience in which the image quality of thestream progressively increases in an intelligent manner. This is notlimited to just scalable encoding; the same experience can be offered byconfiguring a single stream from a low quality stream reproduced for thefirst time and a second stream encoded using the first stream as areference.

[Other Usage Examples]

The encoding and decoding may be performed by LSI ex500, which istypically included in each terminal. LSI ex500 may be configured of asingle chip or a plurality of chips. Software for encoding and decodingmoving pictures may be integrated into some type of a recording medium(such as a CD-ROM, a flexible disk, or a hard disk) that is readable by,for example, computer ex111, and the encoding and decoding may beperformed using the software. Furthermore, when smartphone ex115 isequipped with a camera, the video data obtained by the camera may betransmitted. In this case, the video data is coded by LSI ex500 includedin smartphone ex115.

Note that LSI ex500 may be configured to download and activate anapplication. In such a case, the terminal first determines whether it iscompatible with the scheme used to encode the content or whether it iscapable of executing a specific service. When the terminal is notcompatible with the encoding scheme of the content or when the terminalis not capable of executing a specific service, the terminal firstdownloads a codec or application software then obtains and reproducesthe content.

Aside from the example of content providing system ex100 that usesinternet ex101, at least the moving picture encoder (image encoder) orthe moving picture decoder (image decoder) described in the aboveembodiments and variations may be implemented in a digital broadcastingsystem. The same encoding processing and decoding processing may beapplied to transmit and receive broadcast radio waves superimposed withmultiplexed audio and video data using, for example, a satellite, eventhough this is geared toward multicast whereas unicast is easier withcontent providing system ex100.

[Hardware Configuration]

FIG. 24 illustrates smartphone ex115. FIG. 25 illustrates aconfiguration example of smartphone ex115. Smartphone ex115 includesantenna ex450 for transmitting and receiving radio waves to and frombase station ex110, camera ex465 capable of capturing video and stillimages, and display ex458 that displays decoded data, such as videocaptured by camera ex465 and video received by antenna ex450. Smartphoneex115 further includes user interface ex466 such as a touch panel, audiooutput unit ex457 such as a speaker for outputting speech or otheraudio, audio input unit ex456 such as a microphone for audio input,memory ex467 capable of storing decoded data such as captured video orstill images, recorded audio, received video or still images, and mail,as well as decoded data, and slot ex464 which is an interface for SIMex468 for authorizing access to a network and various data. Note thatexternal memory may be used instead of memory ex467.

Moreover, main controller ex460 which comprehensively controls displayex458 and user interface ex466, power supply circuit ex461, userinterface input controller ex462, video signal processor ex455, camerainterface ex463, display controller ex459, modulator/demodulator ex452,multiplexer/demultiplexer ex453, audio signal processor ex454, slotex464, and memory ex467 are connected via bus ex470.

When the user turns the power button of power supply circuit ex461 on,smartphone ex115 is powered on into an operable state by each componentbeing supplied with power from a battery pack.

Smartphone ex115 performs processing for, for example, calling and datatransmission, based on control performed by main controller ex460, whichincludes a CPU, ROM, and RAM. When making calls, an audio signalrecorded by audio input unit ex456 is converted into a digital audiosignal by audio signal processor ex454, and this is applied with spreadspectrum processing by modulator/demodulator ex452 and digital-analogconversion and frequency conversion processing by transmitter/receiverex451, and then transmitted via antenna ex450. The received data isamplified, frequency converted, and analog-digital converted, inversespread spectrum processed by modulator/demodulator ex452, converted intoan analog audio signal by audio signal processor ex454, and then outputfrom audio output unit ex457. In data transmission mode, text,still-image, or video data is transmitted by main controller ex460 viauser interface input controller ex462 as a result of operation of, forexample, user interface ex466 of the main body, and similar transmissionand reception processing is performed. In data transmission mode, whensending a video, still image, or video and audio, video signal processorex455 compression encodes, via the moving picture encoding methoddescribed in the above embodiments and variations, a video signal storedin memory ex467 or a video signal input from camera ex465, and transmitsthe encoded video data to multiplexer/demultiplexer ex453. Moreover,audio signal processor ex454 encodes an audio signal recorded by audioinput unit ex456 while camera ex465 is capturing, for example, a videoor still image, and transmits the encoded audio data tomultiplexer/demultiplexer ex453. Multiplexer/demultiplexer ex453multiplexes the encoded video data and encoded audio data using apredetermined scheme, modulates and converts the data usingmodulator/demodulator (modulator/demodulator circuit) ex452 andtransmitter/receiver ex451, and transmits the result via antenna ex450.

When video appended in an email or a chat, or a video linked from a webpage, for example, is received, in order to decode the multiplexed datareceived via antenna ex450, multiplexer/demultiplexer ex453demultiplexes the multiplexed data to divide the multiplexed data into abitstream of video data and a bitstream of audio data, supplies theencoded video data to video signal processor ex455 via synchronous busex470, and supplies the encoded audio data to audio signal processorex454 via synchronous bus ex470. Video signal processor ex455 decodesthe video signal using a moving picture decoding method corresponding tothe moving picture encoding method described in the above embodimentsand variations, and video or a still image included in the linked movingpicture file is displayed on display ex458 via display controller ex459.Moreover, audio signal processor ex454 decodes the audio signal andoutputs audio from audio output unit ex457. Note that since real-timestreaming is becoming more and more popular, there are instances inwhich reproduction of the audio may be socially inappropriate dependingon the user's environment. Accordingly, as an initial value, aconfiguration in which only video data is reproduced, i.e., the audiosignal is not reproduced, is preferable. Audio may be synchronized andreproduced only when an input, such as when the user clicks video data,is received.

Although smartphone ex115 was used in the above example, threeimplementations are conceivable: a transceiver terminal including bothan encoder and a decoder; a transmitter terminal including only anencoder; and a receiver terminal including only a decoder. Further, inthe description of the digital broadcasting system, an example is givenin which multiplexed data obtained as a result of video data beingmultiplexed with, for example, audio data, is received or transmitted,but the multiplexed data may be video data multiplexed with data otherthan audio data, such as text data related to the video. Moreover, thevideo data itself rather than multiplexed data maybe received ortransmitted.

Although main controller ex460 including a CPU is described ascontrolling the encoding or decoding processes, terminals often includeGPUs. Accordingly, a configuration is acceptable in which a large areais processed at once by making use of the performance ability of the GPUvia memory shared by the CPU and GPU or memory including an address thatis managed so as to allow common usage by the CPU and GPU. This makes itpossible to shorten encoding time, maintain the real-time nature of thestream, and reduce delay. In particular, processing relating to motionestimation, deblocking filtering, sample adaptive offset (SAO), andtransformation/quantization can be effectively carried out by the GPUinstead of the CPU in units of, for example pictures, all at once.

Although only some exemplary embodiments of the present disclosure havebeen described in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of the present disclosure. Accordingly, all suchmodifications are intended to be included within the scope of thepresent disclosure.

INDUSTRIAL APPLICABILITY

The present disclosure is applicable to, for example, televisionreceivers, digital video recorders, car navigation systems, mobilephones, digital cameras, digital video cameras, or the like.

1-8. (canceled)
 9. A decoder comprising: a processor; and memory,wherein, using the memory, the processor: determines whether intraprediction is to be used for a current block and whether the currentblock has a determined size; when it is determined that intra predictionis to be used for the current block and that the current block has thedetermined size, further determines whether an intra prediction mode forthe current block is a determined mode; when the intra prediction modeis not the determined mode, performs second inverse transform of inversequantized coefficients of the current block, and further performs firstinverse transform of coefficients obtained through the second inversetransform; and when the intra prediction mode is the determined mode,skips the second inverse transform, and performs first inverse transformof the inverse quantized coefficients of the current block.
 10. Thedecoder according to claim 9, wherein the determined mode is anon-directional prediction mode.
 11. The decoder according to claim 9,wherein when at least one of a horizontal size and a vertical size ofthe current block has a determined length, the processor determines thatthe current block has the determined size.
 12. A decoding methodcomprising: determining whether intra prediction is to be used for acurrent block and whether the current block has a determined size; whenit is determined that intra prediction is to be used for the currentblock and that the current block has the determined size, furtherdetermining whether an intra prediction mode for the current block is adetermined mode; when the intra prediction mode is not the determinedmode, performing second inverse transform of inverse quantizedcoefficients of the current block, and further performing first inversetransform of coefficients obtained through the second inverse transform;and when the intra prediction mode is the determined mode, skipping thesecond inverse transform, and performing first inverse transform of theinverse quantized coefficients of the current block.